gross prank I forgot to do.

I forgot to do our new room mate the favor of the "Coffee Prank". When you get a new room mate brew a few gallons of coffee. Hide the liquid in milk jugs somewhere.
Now the prank...
Invent a "House drink" and introduce a pitcher of ambiguous colored liquid.
"We drink this all the time! it fruit and stuff!"
now...
Every time you think about it pour some coffee in the bathroom commode. Be seen leaving the bathroom holding your stomach (don't over act!).
At first your new roomie will be disgusted but not too alarmed.
Then let the roomie see another housemate leaving thin brown water in the toilet.
If you guys are really creative you can create an awful smell that happens with each bathroom visit. You new friend will think everyone has one foot in the grave from punch poisoning!
Won't they be relieved when they find out that they arn't living in the shit house!