Glycolic acid in Pine Sol . . . that's what Jennifer Stalone swore by in her facial cleanser, maybe Pine Sol will do me double duty. (Just kidding) We do have a package of Green Gobbler here, not a clue why we never tried it. Tonight's task, after dinner. Our bathroom sink gets this black stuff all the time, I'm assuming it is fromt the gel toothpaste and gel soaps we use.