Or, in the case of the film 'There's Something About Mary,' the theory that "cleaning your pipes" will steady your nerves before a date because your body will not think you are trying to have sex because you will have tricked it into thinking you have done already...
"Hey Gordon, you should clean your pipes before seeing Jennifer tonight, it'll steady your nerves."
It stings, and that's evidence that it's doing what its name says.
It can also be done right before having sexual intercourse, so you don't get a woman pregnant, and you don't have to wear a condom.
John is Cleaning the Pipes in Cindy's bathroom so he can smash her, rawdog.