Toilets, Sinks, Showers, Tubs and Disposals - Sink leaking from underneath - GRRRR!

I installed a new bathroom sink last night and used all the hardware that came in the box to put in the drain flange and the first pipe down from the sink bowl that connects the sink to the plumbing under the cabinet. I put plumber's putty under the drain flange inside the sink bowl, used the rubber nut underneath and tightened it with the metal nut under THAT. (Note, I did NOT tighten it with pliers or anything because I can't see how to get a grip on a perfectly round edge) All the plumbing beneath that is fine and leak-free from what I can tell, but the exposed threads of the first pipe coming out from under the sink are wet to the touch. I even put a line of silicone caulk around the top edge of the drain flange out of desperation, but 24 hours later, the leaking is still happening.

What did I forget and/or how do I fix it? I need running water in my bathroom!!!!

'used the rubber nut underneath and tightened it with the metal nut under THAT. (Note, I did NOT tighten it with pliers or anything because I can't see how to get a grip on a perfectly round edge)'



That is your problem. Perfectly round edge confuses me......you should have a black washer that bevels up on 1 side. That bevelled side goes towards the sink. A metal washer goes under that. Then a nut..and yes, that nut MUST be tightened with a pair of pliers or it will always leak. Silicon won't save you. And it should be a nut with sides to put pliers on...not round.

See, I didn't want to really wrench on it because I'd read in another thread that it would damage either the pipe or the sink, but a good tightening over some teflon thread tape worked! Running water is a beautiful thing - LOL!