Hello. My little bathroom sink that is a oval 20x17 was leaking so I went out and bought one and replaced it. My first time doing it and a very easy job but I may have made a mistake. When I connected the drain from the old sink to the new sink I noticed that they had not used any plumbers putty. There is a rubber gasket in there and everything was clean. So I did not use any either and now that my sink is installed I turned on the water and the drain under the sink where it comes out of the sink is leaking. Do I need to use plumbers putty or caulking under there or is it the fact that the rubber piece is old and did not seat correctly? Will I need to pull out the sink and start over or can this be fixed without doing that? Im fine with pulling out the sink as I can just re-do the caulking. I just did not see evidence that they had used any putty under there. I have enclosed a photo where the part is. Its at the underneath part of the sink up at the top. At first I hand tightened it and then when I saw it was leaking i added a small turn with a wrench. Any chance it might seat correctly by itself? Here is a pic and thanks for any advice.