flood the volcano

When you're banging a girl and you pee inside her the piss rushes back out as though from a flooded and overflowing volcano

Friend 1: "Tonight I'm going to surprise Becky and flood the volcano. Will make a huge mess but totally worth it."
Friend 2: "Will you be having sex when you do it?"
Friend 1: "Do you think I'm going to somehow stick my totally flacid dick in then piss in her? Use your head, man."