One of the white porcelain undermount sinks that came with my granite countertops isn't quite flat enough around the drain flange area. Thus, even after I installed the drain flange with plumbers putty, a few weeks later and most of the putty has washed out in a small 1/2" area around the perimeter of the drain flange. This is allowing the sink to drain even when the stopper is supposed to be sealing it.
Does anyone have a good suggestion on how to make it seal? The "gap" beneath one part of the flange is probably about 1/16" or less.