I am installing a bathroom sink and this is what I'm dealing for a drain pipe opening/receptacle. I'm hoping that's a drain pipe with a nut rusted onto the end of it, and hopefully with a little bit of elbow grease/WD40 I can spin it off and have access to threads that would be underneath it. Does anyone see any reason why that wouldn't be the case (maybe that's not a nut)?

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  • I would tap that nut with a small hammer. Go all around the outside as well as the face. The objective is to break loose any corrosion. Commented Sep 19, 2022 at 19:58

1 Answer 1


It is a nut. It's the remnants of a compression fitting, as you suspected.

That said, I don't hold out much hope that the threads are serviceable. That much corrosion may have destroyed them. You might need to cut back and sweat on a new fitting.

  • Thanks @isherwood. Going through the wall would be a worst case scenario. I would almost rather solder/braze an extension going into that drain pipe (from the outside) and then connect my p-trap to whatever I solder on there. This is all going to be covered up by a vanity; is there any reason why I couldn't solder/braze/weld something into the hole, and connect the ptrap to that thing? Commented Sep 19, 2022 at 14:43
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    That's more or less what I'm suggesting. I meant to cut back behind the useless threads. Maybe you'll get lucky with them, though.
    – isherwood
    Commented Sep 19, 2022 at 14:55
  • If I am (inevitably) unlucky @isherwood, what sort of pipe/fitting/material would you suggest I try soldering on? Commented Sep 19, 2022 at 15:05
  • I much prefer brass over copper, but I'm not at all sure what's readily available in that size. I don't have much experience with copper DWV plumbing.
    – isherwood
    Commented Sep 19, 2022 at 15:06
  • 1
    Heck, I might resort to JB Weld. :D
    – isherwood
    Commented Sep 19, 2022 at 15:07

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