Referenced in 2 1/2 Men
The "Threesome Episode" where the Sausagefest came before the Clambake.
"Let's lay down some ground rules ...
"Wait, are you sure that everything goes? Even the Philadelphia Dumptruck?"
"Back it up, baby, beep-beep-beep."
Philadelphia Dumptruck, aka, the dumptruck... When a man straddles over a woman's back and puts down a little dna walking backwards.