I've read thru some threads about garbage disposals + p-traps, and would appreciate some help. My P-trap leaks once a year (at Christmas!)

I bought a condo 2-years ago, last year p-trap started leaking when using the dishwasher. The plumber recommended a higher disposal or a shallower sink (to raise the disposal). Instead, we did a quick fix by switching out p-trap and everything was fine.

One-year later and the same issue crops up. This time, I want to fix it properly. The plumber came on the site, and it seems that height of disposal is not an issue. It's slightly higher than the drain.

It seems like I can just get rid of the extra piece of pipe, where there is extra coupling that will fail.


enter image description here

  • Hello, and welcome to Home Improvement. Sounds like you need to fix that leak. And, you should probably take our tour so you'll know how best to participate here. Commented Dec 29, 2019 at 22:26
  • 1
    Have you tried replacing that compression washer inside that coupling? Try one of the softer red rubber ones as opposed to the harder white plastic ones. Even if you replace that piece with one full piece you still have a coupling in the same location which is going to have standing water in it because of the physics of your set up. One option is to tear open the wall and move the drain lower.
    – Alaska Man
    Commented Dec 29, 2019 at 22:51
  • it is not a question of elevation, but a question whether the pipes line up correctly ... try using a rubber trap
    – jsotola
    Commented Dec 29, 2019 at 23:36
  • That piece is slightly longer than necessary, but it is needed to stub-out of the elbow, to provide a means of connection for the next piece. - A new washer (I guess... I don't re-use metal drain pipe, ever) or just re-do in pvc, which comes with washers and won't rust out in 10y.
    – Mazura
    Commented Jan 3, 2020 at 6:41
  • The "this piece seems unnecessary" part is only necessary if you want the sink to drain down the pipes instead of into the cabinet.
    – FreeMan
    Commented Oct 30, 2020 at 13:09

1 Answer 1


First thing to consider is that that connection will always be filled with water, because it's presumably the low side of the trap (hard to tell for sure from the photo, but it should be). So, that connection needs to have extra attention; it needs to be tight, but before being tight, it needs to be perfectly aligned.

One reason it needs to be perfectly aligned is because (I believe) there is often no washer at that connection. My experience is only with PVC drains, but with them, that section of pipe from the waste side is tapered at the end rather than straight, and should not have a tapered washer like all other connections. The pipe itself will be shaped like the washers if this is the case. I think there are a number of different configurations here, so it may require no washer, or a different type of washer, or maybe a standard compression washer.

The extension piece seems to be necessary to align to the waste connection at the wall. If properly connected, there should not be a problem with leaks. It looks like a normal connection.

  • Metal pipes typically use a rubber washer. Another issue with metal pipes is they can get hairline cracks which are hard to see but will leak. Commented Feb 27, 2021 at 16:03

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