I’ve dealt with leaking under the sink before (in the kitchen). The issue now is the bedroom bathroom sink. I have two sinks and I’ve been only using one and not the other, so turned the unused sink’s stop valve to off . In preparation for family’s visit, I turned on the stop valve of the other aink. And I notice there was leaking. under sink leak. Took a picture of my bathroom sink#2 underbelly.

From my kitchen sink experience the nut (#4) closest to the stop valve control was the culprit, so I just needed to tighten that nut while I had my channel lock bite on the nut labeled #2.

But with the bedroom sink #4 nut would not budge when I tried to tighten, while the channel lock grips on the copper pipe #1. I exerted a little more pressure and the whole stop valve assembly (2,3,4) turned clockwise. And it’s still leaking. So I turned #3 counter-clockwise so the whole stop valve assembly straightens up again. Then I turned off the valve and it seemingly stopped leaking. It’s been 10 minutes since I turned off the valve and it has not been leaking (I put a thick cardboard right below it to see if there are water drops on it.
Cardboard placed under stop valve to test for leaks Appreciate you guys’ help on how to stop the leak in the meantime. Will try to replace the stop valve after they leave.

  • You can also rebuild the valve in place; normally the rubber gasket/washer inside has degraded over decades; rebuild kits are cheap and how-to videos plentiful ("rebuilding multi-turn water shut off valve").
    – Armand
    Commented Apr 26, 2023 at 0:43

2 Answers 2


At close look, you have heavy corrosion on the stem of the valve (#4).

This happened on older version of valves.

Now days they use plastic stem that does not corrodes.

You can try cleaning it, first with vinegar to get the caclk, the spray and wait with WD 40.

Eventually you should replace that valve with newer version and plastic stem.

As for wrenching around always hold the #3 firm in place.

  • Is your recommendation for stopping the leak, "You can try cleaning it, first with vinegar to get the caclk, the spray and wait with WD 40."? If so, it would be helpful to highlight that as the answer, expand on it somewhat, and fix up the typos. Everything else seems to be more appropriate as a comment.
    – FreeMan
    Commented Mar 27, 2023 at 14:53
  • 1
    In my experience, it's best to replace the cheap plastic stems with proper brass ones, as the weak plastic can easily snap when turned, leaving you with a broken valve.
    – Armand
    Commented Apr 26, 2023 at 0:40

A valve like this may have a replaceable stem packing seal, but the complete valves are not expensive. I would remove the supply hose and take it with you to your hardware store. Purchase a new valve for what I assume is a 1/2" copper supply and which fits the supply hose.

Don't cheap out. A couple extra bucks spent on a better valve makes operation nicer and improves reliability.

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