bathroom sink leaking

ok i will try to explain this as best as i can, we purchased one of those vanity tops with the sink already in it, all we have to do is put it over the cabinet ok fine but when we hook up all the lines the extension from the sink drain at the top has a bit of a drip underneath the fixture, we have tried everything from plumbers putty to caulking around the seal hopefully this will work, has anybody ever had a problem like this and if so what was your solution?

From what I've read here, put a little plumbers putty on the threads of the tube then tighten the drain locking nut up again- it is leaking around the threads, not under the seal.