Its when your having sex with a chick doggie style over a toilet while she's throwing up from drinking to much.
I gave that chick the drain-o last night after the party.
answers the age old question of how does one piss the shit out of a girl... one begins to fuck a girl in the ass while head and shoulders are on the ground and her ass is up in the air. (very often seen in porn) then one spreads her gaping asshole and pees into her colon. If the pooplets are bouyant enough they will float to the top and spill over, thus pissing the shit out of her. This is an example of unclogging her. other draino definitions explain just the opposite, or some action clogging. Draino is an acid used to unclog, damnit!
see above definition for example. it is possible to do actually perform this. If when fucking a girl in the ass, you see shit on your cock, try the draino and unclog her pooplets. we dont want her to be constipated