I've just installed a new drain assembly from home depot on a new cultured marble bathroom sink. I followed the steps in this fabulous video to prevent leaks, including putty plumbers putty around/on top of the rubber gasket of the drain assembly that butts up against the sink (as shown in photo). Now, it's leaking at that connection.

I also installed a shelf in the vanity a few days after installing the drain, and may have jostled the drain pipe a bit in the process. I'm wondering if that perhaps caused the seal to break, but I also would think that the seal shouldn't be THAT precarious as I wouldn't have applied that much force to it, and it makes me worried what might happen when tenants do god knows what in there.

Should I re-install the drain & plumbers putty and be careful not to touch it again? Or is there anything else I can do to make a better seal in that location?

Thank you!

EDIT: i saw an answer get posted (and deleted?) suggesting that the seal should be INSIDE which was my understand at first too, then I wondered how that worked with the overflow drain built into the basin that leads overflow down to the drain pipe from INSIDE (i.e. below the drain entrance on the OUTSIDE where water normally goes down), which I assumed was the reason for the holes in the threaded part of the drain assembly just a little way down from the drain trim (as in the photo). I figured this is why the black gasket under the basin is a crucial seal and a potential point of failure.

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  • 1
    I think the fabulous video gave you incorrect advice - this seal is either made correctly by the rubber, or not.
    – Ecnerwal
    Commented Jun 12, 2021 at 12:35
  • In addition, plumbers putty will cause staining on cultured marble.
    – Ecnerwal
    Commented Jun 12, 2021 at 14:04
  • @Ecnerwal so you think I'd be better off not using the plumbers putty? I did get the "stain free" kind
    – aknodt
    Commented Jun 12, 2021 at 14:14

2 Answers 2


Plumbers putty (or appropriate alternative) is to be used under the drain trim flange at the top of the assembly, to seal the drain at the sink bowl. NOT at the bottom.

The bottom of the drain assembly should seal to the bottom sink hole by use of a tapered rubber gasket, no putty.

  • 1
    As for the linked video, I will admit that there are often many ways to accomplish a certain task but in my opinion (and by common practice, and as mentioned by @ecnerwal) the lower seal must be accomplished without use of any "sealant/goop" and a seal created by any use of such will eventually leak. Commented Jun 12, 2021 at 14:29
  • Thanks! given multiple responses along these lines, it seems the best thing to do is reinstall it without the plumbers putty. I did put silicone under the drain trim flange per the manufacturer's instructions. I edited my post with an additional photo based on another answer I saw get posted and removed, re needing the seal to be primarily internal. would be curious to hear your thoughts on it!
    – aknodt
    Commented Jun 12, 2021 at 18:38
  • Your edit is correct. The holes in your pop-up assembly are for the overflow. Commented Jun 14, 2021 at 6:12

I had one that was difficult to seal although the original had been good for 15 years. I found the "cultured marble" was rough in the seal area. I sanded it ; 50 or 80 grit , just to take out bumps, nothing fancy . Then the putty and rubber held fine. Apparently the original plumber used a lot of putty and torque.

  • Just went through this after installing new drain - leak. Sanded the bottom of the sink and now the rubber gasket alone is enough to seal. I used 120 grit. Commented Oct 8, 2022 at 20:09

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