I just bleached and mopped out the sludge that collected underneath our basement stairs. The SE corner floods when it rains, and apparently when it does so, it leaves behind this sixteenth-of-an-inch brownish-yellowish stuff in which large white bubbles of mold form if you leave it sit.*

I used one side of the wash basin next to the washing machine as the mop bucket, with liberal amounts of bleach and hot water, and at the end realized I had to stick my hand in the soupy mess stew it had become to fish out the drain plug. Ewwwwwww!

I had no rubber gloves (and who wants to permanently ruin a pair of those on one lousy task?). So...plastic grocery bags. Double bagged. I did not have to put my naked arm or hand in the icky stuff! Yay!

* This was not intentional. We just don't USE the SE corner because it floods, and because it is a dark, cramped little area next to/under the stairs (where some spiders decided to nest in the fall). So I usually have no reason to wander back there and thus didn't notice the sludge/mold until Rainman's PCA moved the litterbox over there.