Forum Title: P trap leaking above trap
Hello, I am installing a new bathroom vanity and sink. My sink has a 1 1/4 drain, however my outlet at the wall is 1 1/2. The configuration I have right now (all slip joint connections) is the 1 1/4 sink drain coming down to a 1 1/4 extension coupling (threaded one end other end is regular pipe). This connects to my 1 1/2 p trap which connects to the 1 1/2 outlet. To reduce at the p trap I used the 1 1/4 to 1 1/2 reducing washer that comes with the p trap. Now for my problem. When I run the sink there are no leaks and everything seems fine. However about 5 minutes later I notice that water seems to be seeping out at the reduction washer and the slip joint connecting the sink to the 1 1/4 extension coupling(which has the wedge shaped washer). The reduction washer is slightly above where the trap water level should be, and the other slip joint is a good 6 inches above that. I am not sure what is causing this back pressure, I would assume that the bigger diameter outlet would theoretically have a lower pressure and would slightly draw the water more that way. Any thoughts?
Category: Plumber Post By: RON VAUGHN (Long Beach, NY), 07/16/2016

is the tail peice long enough into the reducing slip nut washer? is the reducing slip nut washer inserted with the cone down? the threaded tail piece extension, were the threads pipe doped before assembly. NOT teflon tape, but pipe dope? is the trap unlevel? kicked up or in a bind ? ARE you SURE the water you are seeing is not a small leak from ABOVE that connection ? and running down the pipe to pool at that location?

- JOY TERRY (Tigard, OR), 09/08/2017

Hello Frodo, I believe the tail piece is long enough. Although it does not bottom out into the p trap (since the pipe diameter is smaller) there is still about an inch or two of overlap. Yes, the reduction washer is cone down. I have noticed that if I really try and tighten the threaded nut down the reduction washer starts to push up and out of the threaded nut. None of the threads have been doped, my assumption was that these PVC slip joints did not need to be doped. However, I could be completely wrong. The trap is level. This is one of the first things i checked. I am also about 99.99% sure that the water is coming up through the washers and not dripping down. I would run the sink for a while and then sit there and watch the joints for about 5 minutes. Nothing seems to leak at all, you start to notice a little water around those washers about 5 minutes after I turn the water off and then it slowly builds. If it was just the reduction washer I would just assume that the washer doesn't have a tight seal. as that joint is right around the trap water level. However the joint for the extension piece is also doing this, which should be several inches above the trap water level.

- NATALIE PARKS (Killeen, TX), 09/17/2017

No need to dope the threads, that is not where the seal is made. Dope the cone shaped sealing surface on the top of the trap and the extension tube. BUT they should not leak 5 minutes after you have drained the fixture. Are you sure there is not a clog in the line? Does the sink drain rapidly, or is it sluggish?

- GERALDINE FOWLER (Allen, TX), 09/19/2017

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