When to Use Sealants on Threaded Plumbing Connections | This Old House

Making watertight connections with This Old House plumbing and heating expert Richard Trethewey. (See below for a shopping list.)
SUBSCRIBE to This Old House: bit.ly/SubscribeThisOldHouse
Shopping List for When to Use Sealants on Threaded Plumbing Connections:
teflon tape [amzn.to/2N9055D], used to wrap around threaded plastic fittings
pipe sealant [amzn.to/31ctaAs] (a.k.a. pipe dope), used for brushing onto threaded fittings
wicking string [amzn.to/2NU0xnN], used to wrap around and fill spaces between male threads
About This Old House TV:
This Old House is the No. 1 multimedia home enthusiast brand, offering trusted information and expert advice through award-winning television, a highly regarded magazine, and an information-driven website. This Old House and Ask This Old House are produced by This Old House Ventures, LLC and are presented on PBS by WETA Washington, DC.
Follow This Old House and Ask This Old House:
Facebook: bit.ly/ThisOldHouseFB
Twitter: bit.ly/ThisOldHouseTwitter
bit.ly/AskTOHTwitter
Pinterest: bit.ly/ThisOldHousePinterest
Instagram: bit.ly/ThisOldHouseIG
bit.ly/AskTOHIG
Tumblr: bit.ly/ThisOldHouseTumblr
For more on This Old House and Ask This Old House, visit us at: bit.ly/ThisOldHouseWebsite
When to Use Sealants on Threaded Plumbing Connections | This Old House
/ thisoldhouse

[@holdmybeard3160]

So much information in under 4 minutes. This is why This Old House is the best home improvement channel.

[@jonp.6131]

So my dad, who worked with Local 3 in Denver, CO, told me to use Teflon tape and just a thin film of pipe dope after you wrap the joint. It lubricates the threads and you get a better fit up. He also recommended using pipe dope on all threads for this reason

[@justayoutuber1906]

no need to use both

[@JayZoop]

I use both. Teflon always first before dope.

[@campmein]

As always, your videos are awesome, very educational. Richard, you are one “VERY SMART MAN”... I know your knowledge comes from a lot of hard work, and pure determination to ensure the job you do for your customers will meet their expectations. You sir, get a “GOLD STAR” 🌟 ⭐️ 💫

[@popplace4]

I couldn't stop a new threaded valve into old work from a slight leak until I used the wicking technique you demonstrated. Excellent trick and I thank you for your share.

[@iheggis86]

Trebor Eclap me too!

[@c.a.n.4202]

Same with me, 1am and trying to resolve my leak with a second sediment water filter I just added. Tried the wicking technique with some leftover twine for burlap and it worked for me as well. Thank god for internet!

[@f.demascio1857]

Excellent instruction. I'm always amazed at the number of places I see homeowners have applied teflon tape. At least they were aware of the idea.

[@osco4311]

I go with the "tape is a lubricant, not a sealant" theory, and apply it anywhere I want to be sure I can remove connection in the future. Faucets and certain fittings are updated or disconnected frequently enough that I'd rather spend a few pennies on tape that isn't strictly necessary, rather than have to purchase new hoses.

[@Arieeeee]

Perfect! Love Richard.

[@kristopheranderson53]

“Oh yeah, I never noticed that before.” So funny.

[@doobeone]

remember that Kevin was a banker before and he's playing the person that doesn't know anything.

[@mrjoehimself]

Some people just want to watch the world learn, you are those people, thank you.

[@JayKay-ht8rg]

THAT is a very helpful video! Much appreciated. Thanks guys.

[@walrus4248]

Never heard of the wicking before! Thanks for the video.

[@karensimmonds-amyotte2201]

OCT. 2020. Thank you, was installing/replacing a hand held shower head. Thought I might need Teflon tape, but was not sure how to use it, this old house, needed almost ten wrap around before I stopped it from leaking at the shower pipe.

[@kathyern861]

One very important point you failed to make - when wrapping the Teflon tape onto the pipe - you must wrap it in a clockwise direction. Second point regarding the tape - do not wrap the tape beyond the end of the pipe.

[@AngusNB]

1:11 He didn't say it but inferred it by saying "hold the work in your left hand." and showing the tape being wrapped correctly.

[@kathyern861]

@@AngusNB when you are teaching the masses - it is best to spell it out - audibly saying something like "wrap the tape clockwise around the threads of the pipe" - this is always the best method in teaching anyone anything. Many of the people in KZbin are well intentioned, but not the best teachers or presenters. I point out ways to improve - but some people are so hard-headed, arrogant and stubborn - that they think they do not need to improve.

[@AngusNB]

@@kathyern861 I agree, it would have been a good idea to add that detail. "wrap the tape clockwise around the threads of the pipe" Try that phrase on a 20 year old today. Clockwise? 🤣

[@kathyern861]

@@AngusNB Oh my you are so incredibly smart - so much smarter than I will ever be

[@AngusNB]

@@kathyern861 Better sense of humor too. 😁

[@peteryao2008]

Sooo much hardcore information in such a short video. Thank you so much good job!!

[@JonnyDIY]

Great vid! Just what I was wondering. As with many things, "Different Strokes for Different Folks!"

[@dovaz0x]

I enjoyed the show, very clever piece of content!!

[@harindergill7221]

To the point and Very useful video, Thanks

[@sonnco]

Fantastic content as always

[@man_kind]

These videos are fantastic!

[@johnwood2223]

In the UK taper threads for domestic fittings have virtually died out. Pretty much only seen where the radiator unions are fitted. There are a few instances where the are joints with parallel threads. the only way to seal these is too stuff them with tape or the latest silicone impregnated cord, but it's hit and miss and frustrates the life out of me. Taper fittings work 99% of the time and give a degree of positioning, so are a great solution to most joints, so I'd love to see a lot more available on the UK market for domestic installations,

[@jeff95ta83]

You have to be careful using any kind of Teflon (tape or paste) on PVC since it's slippery and is easy to overtighten the joint. Lasco actually recommends not using it, but using a PVC-appropriate sealant.

[@kacatley9258]

Great stuff , thanks guys 👍🏾

[@kurtbilinski1723]

I just installed a whole-house water filter and the mfg instructions explicitly stating not using dope or sealant because it could harm the plastic filter housing. Just putting that out there that it's not always a go-to solution.

[@Zenkai76]

very helpful!

[@javiergalvan242]

Great tips guys!!!!!!!

[@GrimKiLLzGaming]

going to finally start piece working gas and ive done it a bunch of time but by the hour and ive got it kind of down but this is refreshing to see cause i will be on my own now

[@HogRebel]

Good informative video! 😎👍

[@Bigchuck678]

as a plumber, I always use both teflon tape and pipe dope on water connections. Drainage you can get away with just dope, but I don't chance it with water.

[@jaredwaters4633]

Can you over tighten a plastic fitting that thr tape won’t work? I’m working on a water softener and have a mild drip leak.

[@tharindadivakara2881]

Good instructions

[@thomasbroking7943]

Well done. ..👍👍👍👍👍

[@arriegalvan4382]

Thank you.

[@ignusa749]

the one part they missed is that the soft set liquid sealant helps keep the threads so they will move later for rework. so if you have a wc bolts if you use the liquid on the threads as new it will help on holding back corrosion so you can remove or tighten the bolts at a later date. same on the threads for the new style faucet. a dab on the threads help keep it from welding the two metals together chemically. and yes on the yellow soft set harvey's liquid pipe sealer on LP and NG connections for black pipe as well as black to brass connections.

[@mmarczuk1976]

thank u very good video

[@stanskarbek13]

Thanks!

[@audiophileman7047]

Very cool, a plumber I know swears by Rectorseal Tru-Blu pipe slealant. Great info, thank you. 👍👍👍

[@KreemieNewgatt]

The real old-timers use Rectorseal 5

[@audiophileman7047]

I've used RectorSeal T Plus 2 on ABS pipe. It's thicker stuff designed for ABS and other pipes. @@KreemieNewgatt

[@bcummings2187]

Tried them all ....the best is Leak Lock made by Highline Chemicals.

[@davidgoossen113]

Excellent presentation TOH. I too have wondered when to use dope or Teflon tape or nothing. Now I have a better understanding.

[@peterford9369]

Pipe dope also acts as a lubricant to allow a smoother tightening with less friction. As well as filling the threads to form a more liquid seal.

[@Kevscancave]

Great point!

[@peterford9369]

@@Kevscancave Thanks. A very good plumber taught me that years ago.

[@jacobwallace4230]

This is a great video

[@nouralain1]

I believe "Blondie" is asking questions that ppl like me, who have never done this before, might want to know. His questions may seem unnecessary to some but they helped simplify matters for me.

[@d9e240]

My man Richard!

[@DragonBuilds]

I always use tape and dope (Blue monster and T Plus 2) when it is critical that there are no leaks. Irrigation and non pressure systems I just use tape.

[@RTD1947]

Make sure you wrap your Teflon tape in a clockwise direction!!!!!

[@dushk0]

a. k. a. up the thread

[@cav8285]

Just did some research and the pvc manufacturers say not to use Teflon tape on their threaded fittings. Only proper thread sealant that stays soft. Don’t use anything else.

[@eddo1983]

But what if it's reverse threaded?

[@tuxnoel]

If compacted or pressed after teflon tape application, any direction will do.

[@divinecricket3450]

Excellent video and useful info! Quick question: would MOLYKOTE® 111 work as a sealant for the bathroom pup-up drain gaskets? what other options would you recommend? I don't like Teflon tape.

[@ruelsmith]

Wicking is an old technique. I recently replaced my father's boiler, put in in the early 60s but the piping was from 1904, and the piping is all wicked and uses a black type of sealant that sets up hard. Without heat, I actually used a 48" pipe wrench with a 5 ft cheater to get 2" to loosen. Tape, plus dope. That's what were taught in apprenticeship school. Never fails.

[@gchandrasegaran3899]

The black type sealant is called shelloc which is made from natural resin and was used in even today alongwith the thread wrapping in metal gi pipe plumbing.

[@lrocky223]

I use PTFE take to seal threads where needed like described, but I also use it as a thread protection, like anti-seize because most metal plumbing oxidizes over time and can seize threads making it very difficult to break a connection. Is this okay?

[@paulmanhart4481]

Hi. Nice video. Very straight forward. I need to run 3/4” L copper pipe through a bulkhead for my air compressor. Can I use a PVC bulkhead or do I need brass? Any recommendations on which bulkhead to buy? Thanks, Paul Oh, one more question. I’m using Unions in my compressed air lines. Should I use the T Plus 2 on the mating surface, or Loctite flange sealant 518? So many options. Thanks again.

[@craigdaniel3262]

Badass!

[@justsaiyansteve]

Straight dope.

[@jenniferbmendezful]

This was exactly what I needed with great explanations and visual examples.

[@Stingray55]

Great vid. Thanks This Old House HNICs!

[@switchoff64]

Nice

[@Ozzy-87]

In the uk you can get various brands of non setting paste but one in particular called Rocol almost has a consistency of chewing gum and never fails when you paste a gas joint.

[@johnlargue9523]

Good advice for low pressure handyman stuff. High pressure mains I would use different stuff this stuf needs to be buried before you can even test you do not want failures if in doubt use both. America still using NPT type threads?Cheers from Oz

[@ianc435]

Sealer not always needed on pipe thread. For instance. If it’s NPTF. F for fuel. The sealant telfolon is intended for lube in the assembly process. The seal is caused at apex of the thread. Interference deformation.

[@bobt897]

Some thread sealants are incompatible with plastic pipe especially CPVC or ABS. Can soften the plastic leading to failure. The yellow sealer especially.

[@vipleather]

Teflon backed up with dope makes a good sealed high for a long time.

[@therealandrewcano]

I'm thinking of trying that on my next repair. Because just the tape alone I've been having a hard time getting a good seal . 2" scrubber valves

[@kjam87gxp]

so true than typical practice in the pipefitter trade

[@slowedhits2506]

Facts 👍

[@Liberty2357]

I always wondered what to use on that one spherical joint on the P trap. There is no rubber seal there. I usually just use some plastic safe silicone grease.

[@vincentlok8894]

I had to replace an ancient frozen toilet stop valve. It was threaded onto a 1/2 galvanized pipe but the pipe had straight threads and the valve had a washer (which was mostly gone). I could only find tapered thread fittings and didn't realize the pipe had straight threads, and since there is a quarantine on, I could only find Home Depot open. The FIP valve screwed on maybe 1 1/2 turns before stopping (since the straight thread doesn't really mate up). But in desperation I just slapped on pipe done and cranked down hard on the valve. It's not a great solution but I finally got it to stop dripping. I cannot find straight threaded stop valves anywhere! (Maybe cutting and rethreading the pipe is the solution?) Or somehow connecting an adapter...

[@SA-lr1sf]

Thanks. Now I know.

[@ptester1]

Most PVC manufacturers actually recommend non-hardening thread sealant over teflon tape for threaded PVC connections because it seals better and has less chance of damaging the fittings. IME, it works significantly better than teflon tape.

[@54egg]

Great video. One question is how tight to make each type of connection... I know most flex lines tell you how far beyond finger tight... If a fitting leaks, is the dope compromised?

[@kurtvonfricken6829]

Richard, where do you use plumber's putty? Everything!!!

[@jacobkindsvatter4055]

I usually use both tephlon tape and pipe dope on my black iron threads, never use pipe dope on PVC threads pipe dope can actually erode pvc pipe over time

[@patrickb133]

That is plain dumb....

[@kjam87gxp]

I like putting anti seize on steam and condensate unions

[@krakenthrottle2199]

The threads on the National pipe thread (the one that you show on your black iron pipe) are actually what creates your water tight seal, pipe dope or teflon tape help you screw the fittings on a little easier because they provide some amount of lubrication but don't really play much of a role in sealing on black iron pipe with a NPT, if you made a proper thread and the pipe is snugged in it, in theory it shouldn't leak. Also always cut test threads before you start using perfectly good lengths of pipe because otherwise you could waste a lot of pipe before you know there is a problem.

[@MR-nl8xr]

@numberless. What is this " cut test " you speak of.

[@TheNimshew]

Purely a superstition. And if you've been a plumber for 42 years like I have, superstition is good At a U.S. federal prison build, they wanted the dope first, then the tape. The idea being the dope can pick up dirt if on the outside. Actually, I'm heartened to see a lot of quality plumbers tell you that teflon or dope is not a sealant. It is a lubricant to prevent friction when threading two involute circles together. Friction is heat. Heat is bad because the two materials to be joined have different expansion and contraction values. They may SEEM tight when first screwed together, but when allowed to cool will leak. I could screw together some water pipe w/o either dope or tape and after awhile the joints would rust up and not leak. However, the joints would now be as one with themselves and you'd never get them apart. So dope is also to aid in unscrewing fittings!. If only I could post Audel's description of Crane co.'s demonstration using a 10" threaded pipe, putting the pipe in a lathe and hacking away at the threads in various ways. Then screwing it together and putting 425 psi of air and then 1,000 psi hydraulic on the make up with no leaks. I'll try. nope. Anyway, it's in the 1925 Audel's plumbing book. On PDF. If you treat them as a lubricant, you'll never go wrong. Never try to make up voids with either one.

[@TheNimshew]

Max R He's saying to run a thread on a piece of pipe and then make sure the thread depth is right by running a fitting on it. I was taught 3 turns hand tight. Dies get worn or out of adjustment. Just because it was good last time you used the threader doesn't mean it will be this time.

[@TheNimshew]

Numberless Oats. Have you ever read Crane Co.'s test using damaged threads? It's in the 1925 Audel's plumbing and steamfitters guide. Available for free online in PDF

[@jmc5341]

If i made a connection using pipe dope for a hot water heater and its dripping a little bit will tightening it more help or do i have to remove it and re do it. Any help would be much appreciated as i have to tend to this tomorrow morning.

[@50tmack]

I'm trying to connect a metal incoming secondary water line (has threaded female end) to a PVC reducer (threaded male end). This joint has been sealed/ working for several years, but is now leaking. When I take the joint apart everything appears to be in good shape- no visible problems, blemishes, etc in either end. I retaped the male end and tightened w a wrench- it is still leaking through the same threads/ joint. Do you think pipe dope and maybe the wick will actually help, or do you think I need to replace the pieces all together? TIA, Teresa

[@snakeplisken4278]

Interesting. So, do any of you have advice on what to use for boat seacocks pipe connections?

[@scottcates]

Thruhull fittings use straight/parallel threads. It is an all-too common mistake to replaced seacocks with quarter-turn ball valves from the hardware store which have tapered pipe threads on their female fitting. Bad idea.

[@alexgreen121]

Hi, is the T plus 2 PTFE paste good for black pie (gas pipe)? Thanks

[@broadwaymethuen2393]

like a boss

[@Electriclynn]

ALWAYS Always always read the msds sheets and manufacturers guide before proceeding to help!

[@Electriclynn]

Would have liked to have seen gas discussions where immediate pressurization is needed. Word on wrapping anything with tape check if the connection engages clock or counter clock with a quick first fitting test, then proceed in the opposite direction as shown in video 2-3 rounds. Some fittings are bi-directional or counter clock depending on the engineered use… for example, tapped and threaded excess natural gas flow connectors one side tightens left, the other right using 2 crescent wrenches to tighten for proper torque…. And some will require not to exceed a specific torque thus needing a wrench that can measure & stop at a certain torque.

[@Electriclynn]

Much thanks to the team for sharing such a great lesson on a multitude of piping & stuff we use to connect things! Lot’s of work we the people are so grateful to have access without cost! MANY Many many blessings!

[@andreyzagoruyko5390]

Such a DOPE vid . . .

[@kosycat1]

Just spent 3 hours installing a faucet in my bathroom. The 7/8 water feed side would not for the life of me thread onto the facet inputs. The small side threaded on by hand no problem. felt like it was going on straight, would seem to be tightening then it looked like it was slipping off steel braided water line

[@georei]

Get Permabond. It's a pipe thread sealant that can be used on water, gas, or other petroleum product pipe up to 2" It's the best I have ever used.

[@billdowtre7833]

They didn't mention it but iam a plumber and any time I do a water line connection not a faucet supply or flared fitting. I will wrap pipe with teflon first then pipe dope over. This hasn't let me down yet. If you don't want problems use both.

[@johnsmith-fn2kh]

"wrap pipe with teflon first then pipe dope over" Great advice!

[@TheRealFOSFOR]

That sounds completely redundant. If the tape doesn't seal it the don't use it and vice versa. The goo only seals where you put it... I suppose only on the top surface of the tape.. nothing prohibits the tape to leak from other places... I really don't understand people who put tape & other stuff on the same joint.. what is the point!

[@MookieMan1]

The point I️s that it wont leak. Plumbers have been doing this for god knows how many YEARS. If it didn’t work, they wouldn’t be doing it.

[@TheRealFOSFOR]

So it is superstition.

[@CM-xr9oq]

Contrary to what the show is telling us, the teflon dope or tape is a thread lubricant, not an actual sealant. The thread faces seal against themselves, when properly tightened. The pipe dope can help somewhat, if the threads are cut poorly, however.

[@CWillC1972]

I had hoped to see how best to seal the joints on sink connections around the p- and j-trap fittings, where there is a nut with what appears to be a gasket of nylon or teflon. Should pipe dope or teflon tape be applied there?

[@williampeters6004]

My situation or leak it's just like he showed with the compression fitting and that tapered compression going into that nut. I seen that he used pipe dope to help seal it. I'm just concerned that the dope might get diluted from the steam and maybe we'll keep leaking. I tried tightening it but that is it helping no matter how tight I make it

[@debblooth3490]

In your case seems like the cone or the seat is pitted.You never mentioned if it was new or an old style joint,hope that helps.

[@bubblekuku5992]

For thermal installation-radiator pipe with Hemp or teflon tape?

[@YummyPork]

I wonder how many trips to the hardware store this video has caused. Knew I was forgetting something....

[@FrankBenlin]

Everyone needs a Rich neighbor.

[@jaydekaytv]

Is liquid pipe dope or stick pipe dope best for a water heater gas intake?

[@zack9912000]

always use it.

[@josephburkhalter5105]

Please explain wicking string again. What type string? Only cotton? What about valve stems on outdoor faucets? JoeB

[@That7Days79]

Here in singapore.. we usually use the Teflon tape on the water hose even if there's a rubber gasket..😁

[@AStanton1966]

If you doing plumbing without a license you could get caned over there.

[@That7Days79]

@@AStanton1966 haha..no canning but you do need licence to do plumbing as a job...

[@stephenrosenthal5252]

Im an electrician not plumber. But with plumbing fittings ive noticed that it seems anytime you connect brass fittings you most likely won't need sealant or teflon. My guess is because brass is a soft metal and smashes together to make a water tight connection. He pretty much showed that with the radiator, but he didn't mention about the brass. But that seems to be the case when you see brass

[@tigerboy60]

I have a 1 inch cold water supply line attaching to the well casing Male pvc to female metal I didnt tighten it quite enough and I have a small pinhole air leak where the threads meet the metal. I cant tighten it because everything else is glued. What can I do without taking everything apart?

[@theblogofsingh]

Can you apply thread sealant inside csst fitting on the corrugations and the compression sleeve?

[@MrInfoPhilly]

Never

[@ReasonablySane]

Because of the way this video is presenting the information, If I put on my "never done this before" hat, the message is clear: Use teflon for plastic pipes an the dope for metal pipes. Which is, of course, wrong. If you start with metal, continue with metal. If something else needs to be used for plastic, that can be both done and explained WHY it is true.

[@naturekid1335]

I've installed hundreds of boilers. I always tape then dope. Especially when I'm going from old black iron to copper. It's cheaper and less time consuming that filling an entire system, only to find a leak, then have to drain back down and disassemble and redo.

[@AdrianButler86]

Funny how that is common practice as i have seen it done and done it to but the better way would be to apply the dope on the threads then the teflon over it. This way the threads r fully coated and the dope wont easily push itself out. When the dope is put on top the tape it actually more like just a lube to during tightening cuz most of it gets pushed out

[@jayryan7473]

@@AdrianButler86 Pretty sad you aren't aware that dope is DESIGNED to work as a lube so the threads can turn as much as possible for a good seal.

[@AdrianButler86]

@@jayryan7473 who says I'm not aware that dope is designed for easy make up of pipe n fittings? I do know that. do U KNOW that's not it's only purpose?

[@misterindependent7994]

I always wonder about brass to brass. And should guys be using tape or dope on flared fittings. I think not but see it all the time.

[@justayoutuber1906]

no for flared fittings

[@ronniebean7198]

Don’t know if I’ll get a reply but with the supply hose, are there any negatives to using Teflon on those threads even though it’s not necessary?

[@danielcarroll3358]

Probably not, but both sides of the threaded area covered by tape are at atmosphere, not at water pressure, and lubrication is not needed. Note that these are straight threads, not tapered. When you tighten the connection the seal is on the face of the rubber washer not any part of the part you tighten. I often see a similar situation with Teflon tape applied to the fitting on a gas regulator connection to a gas cylinder. In this case the seal is metal to metal and the rotating nut only tightens the connection and has no sealing surfaces.

[@scottydiver5114]

Great video, but I wish you hadn't hid the labels on the type of pipe dope you use I would like to get the same kind you use because I trust you guys to get the best but I don't know what brand you used

[@WatchJason]

What brand of yellow pipe dope was recommended here? There are so many of them out there

[@chrisyerp174]

Good question wandering the same thang couldn't get a read on that bottle

[@sumertheory]

great video. how come when i have a washer in place the pipe connection still leaks?

[@djscrizzle]

Joint isn't clean, washer is damaged, or joint doesn't line up perfectly.

[@cav8285]

Also could be that fitting isn’t tight enough or threads could be mismatched.

[@awqpak]

Nice info in vid. How to deal with a cracked threaded pipe-end in a wall, which is causing seepage.

[@opencoop4268]

awqpak Did you have to replace the pipe? We have a rusted pipe and are trying really hard to get a deal. Any sealant work for you? He haven't had luck yet and I really don't want to replace the pipe which would mean going through a tile wall on some type of fibrous board.

[@toddboothbee1361]

How about metal female thread onto pvc male thread? This pvc threads seem too easily damaged, but I haven't found an alternative. (I'm trying to hook a metal t adapter to my toilet tank.)

[@bigpardner]

How does teflon tape and/or dope stand up to heat, as in connections coming out of a boiler?

[@rupe53]

bigpardner ... teflon holds up in a frying pan, right? It's made for the heat.

[@JohnSmithZen]

What kind of sealant for the threads of a PVC tailpiece??? (the threads right below the mack gasket)

[@cav8285]

Not sure what gasket you’re taking about but just did some research and the pvc manufacturers say not to use Teflon tape on their threaded fittings. Only proper thread sealant that stays soft. Don’t use anything else. Don’t use pipe dope that get hard either. This advice is only for plastic fittings, metal ones are alright to use tape and hard setting dope.

[@kennethlyneham138]

Unions are used in order to make it easy to remove and reinstall something. To use 'dope', or any other sealant is a mistake that only lay people will do. Sealants are adhesives and while they don't dry brittle, they do dry hard. Often that hard that heat is needed to dismantle. If that union joint is dismantled in the future, what you are left with is a very filthy joint that requires a lot of work to get clean again. If the two faces have not been faced properly and there is a leak, only then would you use Teflon tape on the male face but NOT that white rubbish, it is too thin. Either use pink or yellow, (yellow is for gas but not exclusively so). Then when tightened, the joint will be sound and very easily cleaned up after dismantling. Another tip; When applying Teflon tape to a thread, if it is plastic it is better to rough the mail thread up by dragging a hacksaw blade over it at 90 degrees in several places around the thread. If it is brass, use a set of tongue and groove pliers, we call them 'multigrips' and work you way around the thread, crimping little notches in the thread. This will give the tape something to 'grip' and not slip as you screw the fitting together. NOTHING is needed on the thread of a union, as mentioned. The only time I use a combination of thread adhesive and Teflon tape is where the brass thread is very loose and often chromed as well. When the threads a deeply cut and very loose. it is always good to leave them for sometime after screwing home to give the adhesive time to 'go off'. Ken From Lyneham Plumbing Services.

[@readmore3634]

__________________Teflon and or pipe dope is for non-stick. I use pipe dope with teflon in it, and both dope and tape on brass to dissimilar metal. All of this is to keep metal from chaffing inside the joint and balling up. It lets the 2 surfaces slide together so that the METAL ON METAL makes the seal. (Plumbing 101) Teflon and or pipe dope is not supposed to make the seal. It's so you can take it apart someday as well. I use it on every thread (except maybe supply connectors)n so that years later the plumber can get it apart.If you are using this to make the seal you are cutting substandard threads. Rough the PVC threads up?...Crimping little notches in the thread? That's begging the threads to ball up inside....in 40 years of Union trained plumbing I never heard of that!

[@JayZoop]

If I really need it sealed I do Teflon tape first then pipe dope. But always the Teflon first.

[@mrp8488]

Do you ever use teflon tape and pipe dope together? I see some videos where that is done.