Muddy Fire Pit
When a female defecates and wipes from back to front, resulting in a small quantity of feces in her vagina.
John: Dude, her pussy is nasty - she's got a muddy fire pit.
Scott: A what?
John: Muddy fire pit. She got some shit in her snatch.
Scott: A what?
John: Muddy fire pit. She got some shit in her snatch.