Renting out a room -- odor clause in lease?

[Sri June]

Hello, 

I've been renting out a spare bedroom and bathroom on a month-to-month. My most recent tenant had a terrible smell problem: the smell coming from the room was TERRIBLE. It was seeping into the hallway to the point that I'd hold my breath once I got to that floor. 

Now that the tenant has left, I'm trying to figure out ways to remove the stench. I will be charging the tenant cleaning fees since the room was not returned in the same condition it was given. However, the smell persists.

The smell was due to the tenant's body odor. If you walked by him, you could smell the B.O. After he moved out, we realized he also had not washed the bed linens we provided him when he moved in. They're going to get chucked because we can't launder the smell out.

My question to you fine folks:

• How can I remove the smell from the room and our house?
• For future, is there a clause that I can include regarding odors? I would like to prevent this from happening in the future and, if it does, have the tenant bear the expense of odor removal and deodorization.

Thanks in advance!