I have been experiencing a similar problem. About 2 years ago I replaced an undermount sink. After about 18 months I began smelling that sulfer smell when I turned on the water. The sink beside it was not replaced and it does not have any smells. I had tried all the do it yourself repairs with nothing helping for more than a day or two. While walking through Lowes I saw a display for Instant Power Bio-Enzymatic DRAIN STICKS. It says that it ELIMINATES ODORS and comes with a 100% money back guarantee so I thought I had nothing to lose by trying it. I dropped one stick (one of 12 in the pack) down the drain and after about 4 days I realized I was NO LONGER SMELLING THE SULFER. It has only been about 12 days, but so far so good. This may be the best $6 I have spent in a long time! I am thrilled and hope this continues for me and that it might help you too. Good luck!

Timely post. Five days ago I had kohler sink and Pfizer faucet with the plastic drain installed in master bathroom. This morning when I bent over to rid mouth of toothpaste I was hit with an awful rubbery plastic smell. Off gassing of the plastic, I think. Running the water did send the smell swirling around the whole sink. I'm not sure drain sticks will help with that though I am tempted to try.