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I'm trying to install drain plumbing under my sink, and I can't seem to stop the slip joints from leaking.

Here's what I have right now (see picture):

  • coming from the wall is a white plastic fitting
  • very short piece of black plastic pipe (not really visible)
  • 1-1/2" x 1-1/4" trap adapter
  • approx. 6" piece of 1-1/4" tubing, most of which is inserted into the adjoining fittings
  • 1-1/2" 45-degree elbow, with 1-1/4" adapter washers at both ends (see note below)
  • 1-1/4" p-trap arm
  • everything upstream from there seems to be leak-free (including the joint between the p-trap and arm)

enter image description here

I have leaks at the joints on both sides of the 45-degree elbow, and also where the tubing inserts into the trap adapter

I've taken all this apart and re-assembled multiple times, trying to be careful that everything lines up, but I always end up with leaks. Part of the problem might be that when I try to tighten one joint, I end up accidentally twisting another one out of alignment.

Any advice on how to make this work without leaks?

My current thinking is to replace the adapter + tube + 45-degree elbow with a 45-degree adapter. It would have to be a male (i.e., "street") fitting because there's basically no pipe left coming out of the white fitting to fit a female hub, and I really don't want to have to open the wall. If such a fitting exists, that would eliminate 2 slip joint connections. (Edit: I realized a street fitting wouldn't work either. I think I'm stuck with the 1-1/4" adapter unless I open the wall.)

A note about the 45-degree elbow:

The pipe from the wall is angled slightly downward, making an up-hill drain for a few inches. It's apparently been that way for years, and I'm not inclined to fix it (pun intended) unless someone here thinks it's a disaster waiting to happen. Rotating the 45-degree elbow slightly creates a straight connection for the p-trap arm.

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    I would change all the piping to inch and a half. Your problem seems to be the inch and a quarter pipe going into the inch and a half 45. Is there a reason you didn’t go with inch and a half all the way. – Alaska Man Dec 9 '18 at 22:15
  • @Alaskaman good point. The existing trap adapter was 1-1/4", so I went with that, then ended up having to cut if off and replace it anyway. – Todd Gibson Dec 10 '18 at 2:13
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    A lot of people are under the incorrect impression that these are "hand tighten" fittings; they are NOT. Although I agree with @Alaska man in that 1 1/2" would have been right and proper, I will wager that if you tighten all that up with some Channel-lock pliers you're leaks will dry up... – Jimmy Fix-it Dec 10 '18 at 2:39

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