Yes use silicone.
I installed a molded sink/countertop for a friend. The thickness of the material in the drain is about 2.5 to 3 inches, causing the threads of the drain pipe to project into the drain chamber. I have tried teflon tape on the threads but it continues to leak slowly around the threads. Could I try squeezing some silicone up into the cavity prior to sliding the rubber gasket up and tightening the nut?
Thanks. I will give it a try.