Paint the all black. Put in black EVERYTHING, even black light bulbs. And I mean FLAT black, not that funkly shiny stuff. Lots of black towels, too. Even dye the water in the toilet black. Close off any windows and make sure no light sneaks in around the door. In fact, just brick the whole thing up and you'll never have to worry about cleaning it again. If ya gotta go, ask the neighbors real nice if you use theirs.

Simple, wasn't it?