When someone diarreahs in someone else's mouth while wearing underwear, and the underwear filters the solid part of the feces. The resulting filtered liquid flowing through the underwear, and also the actual act, is called a French Drain.
I saw a video of a guy giving his girlfriend a French Drain, and I almost threw up.
by Chris311 December 20, 2006
It is when you pee into your partners mouth,and the remaining pee that flows out runs down their chest.
I totally gave that girl a french drain.
by joe 13 April 26, 2010