Just registered to post that this thread helped me out a lot. I was installing (an admittedly bottom dollar) vanity and could not figure out why I could not get the drain to quit leaking.
Well, first problem was the pop up drain assembly that came with the vanity was made of chromed plastic. So actually, when I was tightening it down, if I tightened enough to really crush the rubber ring, the threads on the top flange piece would just jump off the threads on the drain tube and eventually separate. I forgot about that P.O.S. and went and bought a real brass/chrome drain from Lowes. This one came with a rubber washer to seal the top instead of the usual plumbers putty. Put it all together and it didn't leak as much, but still was dripping around the tapered rubber ring on the bottom. Kept tightening the nut and it didn't seem to help.
Here is how I finished.
1. Took a coarse sanding pad and gave the drain hole a real good rub down. The hole was not perfect when I was done, but the rough edges were gone and a place were it was chipped out was much less vicious of a gap too.
2. Plumbers silicone grease on both sides of the flat washer between the nut and the tapered rubber ring that seals the bottom.
3. Teflon pipe thread dope on the top and bottom drain pipe threads, and also on the sealing surface of the tapered rubber ring where it squishes into the bottom of the vanity.
4. Took the vanity off and tightened the nut down onto the tapered rubber ring until it hit a stop!
After this, it no longer leaked. Thanks for all the tips!
Edited by runderwo (06/26/12 10:19 PM)