I purchased a new bathroom sink and faucet and set everything up according to instructions. The faucet instructions told me to use silicone for the drain lip (the border thing around the stopper in the bottom of the inside of the sink, flange?).
Anyways, underneath where the pipe comes out is a rubber gasket and I've used the plastic screw on the drain pipe to seal the gasket against the underside of the sink, but when I put a little bit of water in it, some water leaks out from between the gasket and the sink. I've tried tightening it as much as I can and it still leaks.
Should I be putting silicone or plumbers putty between the gasket and the sink? If possible, I'd like to avoid taking the drain lip off because I've already sealed it there. What should I do?
Here is a picture of the underside of the sink:
UPDATE: It turns out (haha) that the problem was that the rubber "washer" was actually threaded itself. I'm not sure if they are always like this, but I didn't realize that it was threaded when I was assembling everything. So I assume that what was happening originally is that when I didn't have the rubber washer close enough to the basin when I started tightening the nut (blue) that it was moving the the threads out of alignment or something and not making a good seal. Once I turned the washer a few turns upwards, then tightened the blue nut, it made a proper seal. All without using a bunch of putter or silicone.