Re: Odd black mold like substance in sink drain
It sounds like what you are describing is a biomass. Often the initial complaint is that the water smells. What you are really experiencing is air being driven up, out of the drain into your face.
This biomass is most often found in bathroom sinks. If this is the case and you don't have it at all drains, the cause is most often make-up. Also some of the fancy soaps.
I have had to pull the trap and ream it out with paper towels to get it out. Bleach dosen't even seem to help. The only thing I have found that really works, is to take it apart and clean the trap.
Be warned. Some of that stuff can get really nasty. Wear disposable gloves and work over a garbage can.
Waste not, want not.
Use it up. Wear it out. Make it due, or due without.