If no matter how tight the nut is and it still leaks take everything apart including the drain pipe and the drain outlet flange in the sink.
New bathroom sink drain leaks at threads.
After taking the bathroom sink drain outlet flange and drain pipe out inspect all parts to see if it may be cracked or if the plastic or metal threads are stripped.
I cannot get my bathroom sink drain to stop leaking specifically from the doomed rubber gasket area where the threaded tailpiece comes through.
The leak is coming from the nut where the drain attaches to the bottom of the bowl so you tighten the gasket to the bottom of the bowl.
Insert the drain back into the hole making sure it s centered.
Wrap a half inch thick putty ring around the the top of the drain flange.
The bathroom sink drain leaks into the vanity.
Turn the water to check for leaks.
You must seal the area between a sink s drain body and the actual sink surface otherwise water will leak out between the two and begin dripping under the sink.
Tailpiece leaks the tailpiece attaches to threads on the bottom of the sink drain at its top end.
It attaches to the p trap on its bottom end with slip nuts and washers.
The plumber at one of the big box stores told me that i couldn t use a pop up drain assembly with the holes for an overflow if my sink doesn t have an overflow.
Remove any excess putty from around the drain.
Apply plumber s tape to the threads of the drain union.
Sink drain popup leaks drip due to the threads of the lower half of the popup assembly making a channel allowing the water to drain out.