I think th eheaters are disposable(the pocket heating ones you break and shake?)
I had to do this once and the chick stood at the door while I did it.

True story,I worked security and Me and my coworkers Smoked alot.and we finished work and my buddy used are company bathroom and when he came out,he came out laughing hysterically.....he told me he saw someones pee cup on the sink,he told me he emptied it out and filled it back up with his piss,and that whoevers it was aint gonna get hired.a few weeks later after we hired a new guard,My boss told me that one of the applicants that he was hoping to get hired,failed his drug test and that the guy was denying it the whole time.
So....Dont leave your cup in the bathroom unless they tell you to.