nasty sack

A term used to describe the sexual act of dipping one's own nutsack into a toilet filled with bean burrito-induced diarrhea, and then allowing one's sexual partner to clean the fecal matter off of the scrotum using their tongue.

"Come on, nasty sack!"
"I still can't get the taste of Gud's diarrhea out of my mouth. He gave me a nasty sack last night."