you still have to live here for a while. As much as it might seem good to do something evil to get back at them, use common sense and realize that it will only cause more trouble. I would call a meeting, calmly tell them the problem and then volunteer to always clean the bathroom--for a price. If they pay you, then yes you will clean up after them. If that doesn't work, try collecting all their filth in a bag and depositing it on their beds.