[holly412]

Black stuff coming up from sink in powder room, husband put something down from home depot did not work I put bleach and still comes back not as much but still there

[Milo Dolezal]

Most likely, you have blocked drain: remove P-Trap, insert small hand snake and clean the pipe as it enters the wall.

Also, the blockage may be in the sink drain itself. Here, remove P-Trap and pop up piece. Look down into the drain. If you cannot see through than it needs to be cleaned, too.

[afaroo]

And here is another image how to unclog the sink drain, good luck.
John

[KenSayers]

That much I know. I can clear it. What I need to know is, "What is it?" Can it be that "black mold" that everyone is afraid of?