Those first two answers are right. But, now don't laugh! Sometimes people say that when they haven't been able to go to the bathroom. So they go to the store and buy a laxative to "clean them out". This topic would not be a very glamorous subject in a movie, but real people do have these real problems sometimes. Maybe not in a movie would you hear this topic, but you might hear someone in a pharmacy tell the pharmacist they need something to clean themselves out.