I installed a new PVC tub drain on a fiberglass tub because the old brass drain was leaking. The new drain is leaking on the bottom of the tub even with a new gasket. The new gasket seems pretty thin. Should I try doubling up on the gasket or adding silicon caulk - or any other ideas?

Did you use plumbers putty under the drain basket on the inside of the tub? Did you put pipe thread compound on the male threads of this same basket? Do not use caulk. Have you verified the tub is not cracked?

Doug has nailed the likley problem. Many first time DIY fail to put the plumbers putty on the drain, that's my best guess of the problem.

I did use plumbers putty - but did not seal the threads. I can't find any cracks in the tub. I will try again with a different gasket underneath the tub and add thread tape. Thanks for the help!