When your feces is so watered-down that excreting it is similar to urinating out your anus. Generally the result of food poisoning, stomach flu, or using way too much lube for anal.
"After eating the nasty Vietnamese food, she was buttpeeing for days."
by seemo March 19, 2007
When your poo has the consistency of pee.
After drinking a case of Old Milwaukee, Jeff had a serious case of butt pee.
by Erock April 06, 2004
Liquid emitted from the anus, such as after receiving an enema.
"Ivy's pants were soaked with butt pee after her anal cleansing."
by pr0nographer March 08, 2010