I replaced a bathroom sink, when installing the drain I used plumbers putty as per instructions,I filled the sink with water to check for leaks, but where the rubber gasket on the bottom of the sink is tightened with a large nut it appears to leak through the threads. I don't want to tighten it much more in case I break the sink. Is it the rubber that is defective or a warped sink or something. :confused:

Perhaps the rubber gasket is in cocked. Pull it apart and install it again. Regards, Tom