The act of shitting into the tank (or upper portion) of a toilet. Done as a prank, it results in at least four foul flushes (also known as a "3-F qualifier") afterwards.
"Man, I'm gonna fucking puke."
"Dude, how come?"
"Man, someone dropped an upper decker in the toilet, and the water splashed my ass and sack."
"Dude, that sucks."
"Man, I think I got a piece of corn stuck to my sack!"