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 puttey or silicone.
UPDATE2: So it has been 10 months and it hasn't leaked. Problem solved.
UPDATE3: It's been 8 years and it hasn't leaked.
Best Answer
It should not be necessary to try to goop some type of sealer around the lower neck of the sink drain. Such solution may work but it is not the desirable approach when you consider that someday this assembly will need to come apart for repairs.
In looking at the assembly that you have I wonder if one or more things are at play here.
1) If the drain pipe tail was not centered in the neck of the sink drain and then had lateral force on it due to the down stream goose neck trap it could be forcing the gasket open on one side. Check that there is no undue large amount of sideways pressure on the lower part of this pipe assembly.
2) It looks like the gasket directly contacts with the face of the capture nut around the drain pipe. It is possible that by tightening the capture nut that it is putting a twisting force on the gasket that may cause it to "fold away" from the sealing edge of the sink neck.
3) It is possible that there could be a small crack or pitted area on the sink neck that keeps the rubber gasket from engaging 100% with the sink neck.
4) Sometimes the "rubber" used in this type gasket is made of a plastic material that is anything but rubber. Check at the local hardware store to see if they have another gasket that is more pliable. In some cases a silicon material may be better.