I am replacing a pop up drain in the bathroom. It seems the rubber gasket is not totally sealing the basin opening. Do I need to fill in with silicone sealer or plumber putty? Or, heaven forbid... am I doing something wrong? I've removed and reattached and keep getting the same result. HELP!!

Put plumbers putty between the drain flange an the sink.

What about where the sink basin and the rubber wedge meets. Would a shmear of plumber putty help that seal better.

No, just put putty between the flange and the surface of the sink bowl.
If you have trouble with a leak between the seal and the under side of the sink, get another pop up assembly, the rubber gasket seems to be a little small on some models.

Sometimes you really need to tighten the nut to make the leak stop. Putting a bead of silicone on the top of the washer would help.

And here is a exploded view. Good luck, Tom

I don't like silicone in cases like this unless you don't use the sink for 24 hours. Instead, pipe dope on the threads that pass through the sink and the washer and nut tighten up and over, works really great! Overtightening the nut can work sometimes, but can also cause the washer to splay even more so watch for that if you try to tighten more.



Mark

I once went through 3 popups and two sinks to get a leak sealed. Think the real problem was that some of the bath sinks are imported and the drain hole is a little larger. Of course it could have been that I was over tightening.

The thing I dislike the most about home center faucets, is the plastic pop - up assembly. It can be difficult to achieve a water tight seal at the bottom gasket, especially with a cultured marble sink. Over tighten the nut on the drain shank, or pivot rod, and they will break.
We buy 17 gauge, chrome plated brass alloy pop - ups from Wolverine Brass company as a substitute for the plastic version, and like Mark, we paint the shank thread & bottom gasket with pipe dope during the install...

Yup! Funny enough, we usually throw out the plastic pop-ups and install the WB brass pop-ups at my shop, too... NEVER have a problem with these!