[everyman46]

All through the fall and winter, my master bathroom sink flows free and clear..no problems. Now spring has come, and periodically from now through the summer I will get a build-up of a black, almost tarry gunk that grows up around the plastic sink stopper support, the flanged shaft that connects the round sink stopper to the push rod that comes into the drain plug. I have to take out the stopper, clean off the shaft, and hook it back up which is kind of a pain to keep it from clogging up. Any ideas on what it could be and how to keep it from forming? I'm thinking some kind of mold but it doesn't smell moldy or smell at all for that matter.