I'm replacing bathroom sink drain assembly, but it's slowly dripping the water. The assembly is old. I only replaced washer. It tightened with hands. Any ideas?
The key to a good seal is to make sure that you get a really substantial bead of plumbers putty all around under the sink flange. As you tighten the nut under the sink the putty will ooze out around the flange in the sink. Just peel it off and you should be good to go.
The nut underneath does need to be tight but it shouldn't require an excessive amount of torque.
I don't always use or recommend plumber's putty for drains any more because it eventually dries and cracks. Then the task has to be repeated and i don't like unnecessary repeat tasks. Many will say this is sacreligious but clear silicone kitchen and bath caulk is the more modern way to go. It remains flexible and won't crack.