Hello.

I installed a new garbage disposal and when I went to reattach the PVC p-trap to the drain elbow, I can't get a good seal, and a leak persists that flows out of the underside of the nut that connects the two. The nut is attached to the p-trap and seal upwards to the threads of the drain elbow.

I'm afraid I might have damaged the nut slightly when removing the disposal but it still seems to tighten along the thread of the drain elbow without any issues. I'm confused as to whether a cracked nut could actually result in a leak since the nut floats freely from the "inner" pipe-- it is only ensuring the seal of the elbow and p-trap and doesn't appear to me to be involved in the actual flow of water. Plus the nut seems designed to have air between it and the inner pipe even when it's tightened, so this makes me the think the the nut isn't the problem, that somehow I'm not getting a good seal between the actual pipes. But the nut is tightening, so I'm going in circles!

Could a micro-crack or similar in the nut cause this leak, even if the seal between the p-trap and the elbow appears tight? There's some physics going on that I'm not quite getting. I should mention that there was no washer connecting the two, I'm a novice so not sure if that is standard (but I was told at a store that it's normal for this set-up).

Driving me a little crazy, thanks for your suggestions

Dave

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Edited 1 times.

& pipe dope pipe dope pipe dope. never have leaks with that stuff - messy but great

Pictures would better help.

This is the trap's UNION nut which does not use a washer. But that type of trap typically does NOT respond well to being disturbed and then reassembled. I, and many plumbers, would cut it out and connect with a different type of "P" trap.

These nuts are notorious for cracking when over tightened. I normally cut the ABS Pipe and put an mips adaptor and use tubular fittings to make the connection. It works well for me. But even then when you have plastic nuts if you over tighten you are asking for problems. With experience you will learn how much you can tighten the nuts.