this morning i awoke to find the kitchen sink filled afew inches with black gunk! It had come from the overflow and was tar black with bits and pieces of what looked like cardboard. It smelt like perm neutralizer. I cleared it away and blesched the sink and overflow then put mr muscle drain unblocker down the over flow (the one for standing water in the orange bottle). Please advise as I don't know where to go from here or what it was!!