Method 1. Cleaning Porcelain Sinks. Start with a gentle sponge and dish soap. Wipe the sink down with baking soda. Coat your sink with bleach, then cover it with paper towels overnight. Use vinegar to remove watermarks. Try other specific, non-abrasive cleaners. Use lemon juice and table salt to get rid of rust stains.
I have found the best and easiest way on how to remove stains from a porcelain sink! I feel like I hit the jackpot of cleaning with these tricks and tips!
Spray bleach or a bleach product all over the sink. Let the bleach sit for a few minutes while you try to wash off the little bit of bleach that went on your shirt. Gently give a general scrub all over and rinse thoroughly again. After this step the yellowish color was gone but the black stains were still there.