I have a slow leak under my kitchen sink, in what I think is the top-most screw thread in the photo below. It leaks when the sink is full.

EDIT: specifically, I think the leak is between the gray sink pipe and the off-white pipe right at the top.

enter image description here

I am very practical (carpentry and such) but have zero plumbing experience. Even with sinks.

Can I "just" buy some parts and connect them up? Like water lego


  • Hello, and welcome to Home Improvement. Does it leak when it's draining, or even when it's stopped? Where does the stopper go? (A picture from the top might help.) Apr 18, 2019 at 1:37
  • Meanwhile, put a low pan, basin under there. We use a restaurant bussing basin -- the gray things that busboys use to collect dirty dishes. The last leak I had under the sink went undetected for several months, and I ended up replacing half the kitchen subfloor. Double plus un fun. I now keep that basin in there under the sink. Just 'cause. Apr 18, 2019 at 19:38

2 Answers 2


Are you talking about the threaded joint between the white pipe and the gray pipe leading down from the sink? You could just try snugging the joint up by turning the nut clockwise. If it is loose you can do it with your hands and then just snug it up with a large pair of slip joint pliers or a pipe wrench. Be careful not to over do it and break anything. All those joints are like compression fittings. The mating ends of the pvc pipes are compressed against each other by the plastic nut that you can see on all the joints.

If the joint is just seeping, chances are that just a little tightening will stop it.

If you are talking about the black pipe that connects to the bottom of the sink you may have to loosen the nut connecting the black pipe to the gray one so that you can tighten the black pipe up against the sink. There is a threaded pipe inside the sink (the metal pipe that the sink stopper goes in) that threads into that black pipe and holds it firmly to the sink. Normally plumbers putty is placed as a sealant under the flange of that pipe, which is then inserted into the drain hole in the bottom of the sink and then threaded into the black drain pipe you can see in the photo.

Again, a little snugging up may be all that is needed to stop the seeping water. If not you will have to disconnect the plumbing under the sink so you can remove the drain pipe from inside the sink and reapply plumber's putty and reinstall. Look for Youtube videos about installing sinks for more details.

  • Thanks @Genki. I have tightened that nut with my hands already, and don't have a big enough wrench to get it any tighter. You think it's worth investing in one?
    – mafrosis
    Apr 17, 2019 at 22:18
  • 1
    Compare the price of the tool to a plumber's hourly rate or house call rate. Plus you get to keep the tool. Definitely worth it.
    – Genki
    Apr 17, 2019 at 22:23
  • 1
    Where exactly is it leaking?
    – Genki
    Apr 17, 2019 at 22:24

You could try applying silicone to stop the leak (make sure the surface is dry before applying it). It's not the "right" way to fix it, but it's cheap and easy, and it should last for years, especially if there is no movement under the sink.

  • If it's leaking only when the sink is full, implies that it is shifting under load. Apr 18, 2019 at 19:37

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