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My bathroom sink drain began leaking recently. The PVC connection that meets the ABS connection is the culprit. See picture with red arrow below.

After taking everything apart and cleaning the parts, I discovered the ABS threads look to be dented (see picture). I suspect the leak occurs because the tapered gasket cannot form a water tight seal where it meets this dent.

How do I fix this?

  1. Can a material of some kind be added to fix the dent, but still allow the threads to work?
  2. Do I have to replace the ABS thread connection entirely? I'm not sure how to do this exactly since I believe ABS connections are cemented. Guidance is appreciated if this is my only option.
  3. Other?

It looks like there may be a glue type residue on the ABS threads. I wonder if there was once glue of some kind that broke down over time and caused the leak now. I can't imagine why this connection would have sealed without some kind of other stop gap measure in place to account for the dent.

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Try @JACK solution of cutting off bad threads. You might also try a different style slip-joint washer (they come in plastic or rubber). Tighten the fitting, hand tight is not enough. If that doesn't work, the fitting is toast. I would cut it off and glue a new one on, then use the proper slip-joint assembly with no glue, goop, caulk, goo, or any other such nonsense that is unlikely to work.

You have a couple problems though.

  1. If you cut it off (even if you cut carefully, which you should) there will be very little pipe remaining outside of the wall. That's OK though, glue the new (1 1/2" male adapter) to whatever is left and it will be fine. Use abs glue if you get an ABS fitting, use universal or multi purpose glue if your new fitting happens to be PVC.
  2. The PVC trap arm may end up being too short after you shorten the wall pipe (it depends how much was left inserted into the wall pipe). If so, you'll need a new P-Trap.
  • I think your answer was posted while I was at Home Depot getting the replacement ABS parts, but the numbered steps are what I ended up doing. I cut the old ABS connector off, attached a coupler to what was left coming out of the wall, added an extension 1-1/2" pipe in case the future needs it, and finally added a new threaded end for the PVC to attach to. – Scott Lin Aug 17 at 0:55
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I would use, and have used, a sealer designed for plumbing systems that is designed not to harden and stays sticky - works a treat.

I think it is called plumber’s mait

But it sticks to your fingers as well... seal the joints with it and you don’t have to tighten the threads much. Think about how the joint works so you don’t apply too much ie work out where it is most effectively applied.

  • Is this plumber's mait the same a plumber's putty? Do you know the name of the product at Home Depot or Lowe's? I can't find much online for "plumber's mait". Thanks. – Scott Lin Aug 16 at 21:39
  • I gave you the name of the product I use. I described the product. I do not shop at Home Depot or Lowe’s. It does exist online - check the Screwfix website. – Solar Mike Aug 16 at 21:42
  • Ah, I see the disconnect now. This is a European product not sold in the USA (as far as I can tell). Thanks for the recommendation, but it looks like I'll have to find another product. – Scott Lin Aug 16 at 21:50
  • Well you did not state a location and that black pipe and the white ones look just the same as those here in Switzerland... There are many similar products, but crucial to all is working with the joint in how it is designed to work. – Solar Mike Aug 16 at 21:54
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I'm guessing you're going to get a few opinions on this so I'll start out by saying what I'd try. I'd get one of those rotary tools with a cut off disk and start cutting right where the dent ends and cut all the way around the circumference of the fitting. You might be able to do it with a hack saw blade. Then I'd chamfer the inside edge with some emery paper or a round file until your tapered gasket fit in there. You might still have to add a little caulk between the fitting and the gasket depending on how well you smoothed out the fitting but at least your threads would still work.

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Here are several ideas that came to mind.

(attempt to) Repair the threads

Heat will soften the black ABS so you could improve its shape, but it's probably not realistic to hope for sealing with this alone.

Augment with plumber's putty

Roll a rope of putty with thickness similar to the gasket and wrap it around the PVC so that it contacts before the gasket. Maybe this will do the job, especially if you can at least partially re-shape the ABS so the dent/gap is smaller.

Alternate connection

A 1-1/2 PVC female adapter from the Big Box Sprinkler Department will seal against the threads rather than the face of the ABS male adapter. Brush the threads with pipe joint compound, install the female adapter, then figure out how to adapt from the PVC slip joint to the PVC drain tube. I'm not sure whether the OD is the same such that the drain tube could be cemented directly to the female adapter..

Replace the ABS fitting

You're right, this is solvent welded to the pipe in the wall. It can be removed with abrasives such as a sanding drum on a rotary tool ("Dremel"). The plastic will wear away quickly with a coarse grit but it'll be tedious because of the difficult access. Depending on how the vanity is attached it may be worth the time to move the cabinet aside -- with good access that original fitting might be sanded away in under half an hour.

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