I let a friend stay with us for a while. She was struggling financially, so I was helping her get back on her feet. I didn't charge her anything to stay with us, of course, but I did tell her she needed to clean up after herself (which included keeping the bathroom, that only she used, clean) and help with a couple other chores.

She moved to her own place yesterday, so I went into the room and bathroom she was using to make sure everything was fresh and tidy. This is what I saw when I stepped into the bathroom. The pictures don't even do it justice.

My husband and I have tried cleaning a small spot, but it has hardly made a difference. We have tried our normal cleaning products, a strong bathroom cleaner with bleach, and a good toilet cleaner with bleach.