We had this problem a few months ago but the young man was placed here by an agency while they were looking for permanent accommodation for him. We had to ask him to leave after a few days as the access to all our rooms is through an internal corridor and everyone who entered was affected. The agency was charged and they paid for the cleaning and the replacement of the mattress. Sorry that probably doesn't help you unless he was through an agency, in which case they will understand if you just say no. The only thing I can think of is to try and start a conversation about the problem and see if he is aware and/or if he has a solution. Otherwise I can see him turning up again and again and the problem repeating itself forever. Good Luck. Stephanie