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Old 01-27-2013, 06:22 PM   #1
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1959 24' Tradewind
Quantico , Virginia
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Dump Valve Threads


The black water dump valve on our '50 Tradewind was leaking between the threads above the dump valve and the 3" female fitting on the bottom of the black tank.

I took the valve and male threaded fitting out, cleaned them up, replaced the 2 seals.

Question, what do I use to act as a sealant between the 3" pipe threads? I tried liquid Teflon. Leaked. Looks like the previous owner used silicone.

Which sealant is best?
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Old 01-27-2013, 07:39 PM   #2
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I am not a plumber. I don't want to be a plumber. Having said that, I have been forced to do some plumbing in my life and I was mad before I started. But, if that 3 inch object is metal, thread dressing comes in liquid form with a brush applicator and also comes as a stick which can applied much like chalk across the threads. If it is PVC I generally use teflon tape, in this case a whole lot of teflon tape. I suppose teflon tape could also be used even if it is metal. I am just glad it is you doing it and not me!!!!! Good luck.

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Old 01-27-2013, 07:46 PM   #3
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I can't think of the brand name right now, but it comes in a white can with red letters. It's something like REXALL. You should get pipe dope. When you do, make sure it can be used on PVC PIPE.
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Old 01-27-2013, 09:14 PM   #4
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It is important to clean the threads carefully. A wire brush works well. It may help, on the metal threads, to use a solvent of some kind. WD-40, brake cleaner, nail polish remover, whatever.

I use Rectorseal #9 slow set, which is a paste compound available in most hardware stores and home centers. I apply a moderate coat to male threads and a light coat to the start of the female threads.

Sometimes, for difficult joints that are prone to leakage, it is helpful to apply a light coat of Rectorseal #9, then wrap the joint with teflon tape, then apply another light coat of Rectorseal #9. It's easy to crossthread the joint at this point so be very careful when starting the threads.

There are a number of alternatives if that doesn't work. For one, you can replace the threaded flange on the valve for around $5, which may help if the plastic threads are in poor condition.

Another step to try is to use a 3" pipe tap to chase the threads on the black tank. They are prohibitively expensive to purchase but rental places sometimes have them or you can pay a plumber who has one to do it for you.

Or you can try making an ersatz tap out of a 3" diameter steel nipple by grinding some slots in the threads to allow scraping action to occur.

Failing that you can try a 3" close steel nipple, which may seal to the old threads better than the plastic, and then replace the male 3" flange on the valve with a female 3" flange, which is readily available from Valterra.
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Old 01-28-2013, 06:27 AM   #5
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I used rector seal T+2. Still had a slow drip between the threads. Is there a pipe sealant out there that expands as it drys but wont form a permanent bond? (in case this valve needs to be replaced later?
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