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RTV for plumbing?

About six months ago, I had to replace the tank on my well. On the output side, I used a 1 1/4 threaded x solvent PVC union, then a 1 1/4 x 1" PVC bushing and then 1" PVC pipes and fittings to the house. At the time, the adapter leaked at the threads of the union and the tank bung. I went through three unions before I finally got one that didn't leak.

Last night, water is pouring out from under the well cover. This morning, I pull the cover and find that it is leaking again at the union to bung interface. It was leaking so bad, I thought the union had cracked but when I removed it, there were no cracks.

So i got a 1 1/4" to 1" threaded galvanized bushing and screwed it into the bung, then I used a 1" threaded x solvent PVC union and it seems to be holding.

But if it starts leaking again, I am thinking of using Ultra Gray RTV instead of teflon tape on the threads. any reason why this is not a good idea? Has anyone used some type of RTV on a particularly persistent leak?

A. Spruce
Re: RTV for plumbing?

I recently came across someone who said that teflon tape isn't actually intended for sealing two surfaces, it's main purpose is to reduce friction which allows for an extra turn or two of the fittings, creating a tighter seal due to tighter tolerances, as opposed to plumbers paste that does actually take up gaps and such. I have not verified this information yet, but it does actually make sense if you think about it. Also, most installations of pvc pipe and fittings recommend NOT using teflon tape in the connection, which again, indicates to me that the point of the product is not to seal, but to ease friction, a trait with pvc fittings that can cause over torquing and breakage of the fittings.

So what can I say other than to do some research into the purpose and uses of teflon tape before you use it. On top of that, it would also seem that pvc fittings in the environment/purpose that you are trying to use them isn't working, so why keep trying to use it? Instead, use galvanized or use brass fittings, both of which recommend the use of both teflon tape and plumbers paste.

Re: RTV for plumbing?

Around here we use NSF Poly Plastic Pipe, a black flexible pipe and brass fitting. I would never use galvanized or plastic fittings of any type on a well system.


Re: RTV for plumbing?

I like to use a teflon-containing thread sealant compound that is listed as "safe for plastic." Some of the older formulations contained solvents that could damage plastic.

In spite of that, I find that the quality of workmanship of plumbing fittings nowadays is somewhere below rock bottom. It's nearly impossible to get a good seal anymore. But then again, most of those fittings come from a large, communist country on the other side of the Pacific where the workers have no pride, the companies have no standards, and the government has no morals.

Re: RTV for plumbing?

I did use the teflon thread sealant the last time and it held until the night before last. I should not there there is an identical bung on the other side of the tank for the inlet of the water, it has the same setup but it has never leaked. It has teflon tape on its threads.

I suspect that the bung got ever so slightly distorted when it was welded to the tank. I also think the threads have a burr in them somewhere that is damaging the threads of the PVC unions. I wanted to get a brass bushing but we only have a small Home depot here to get supplies at so I got a galvanized one. The steel is probably holding the threads of the bung true now.

Anyway, what about RTV? Opinions?

Re: RTV for plumbing?

RTV would probably work but I'd be worried about it leaching chemicals into the water supply so I wouldn't go there. Alternately you can use epoxy (I prefer JB weld). Again you need to let it harden at least 4 hours but it's nowhere as chemical laden as RTV and as far as I know it's safe for potable water once hardened. It will create a permanent connection so you may want to stub something you can remove past it. I've used JB weld for leaks on old WH's with rusted threads and it's never failed me as long as I had a decent mechanical connection.


Re: RTV for plumbing?

Good idea Phil. I didn't think about JB Weld. This is a bushing to reduce from 1.25" down to 1" so if I can use something that will work, it is OK for me if it is permanent. The leak is always around the 1.25" threads and it is the only connection that has leaked.

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