The act of taking a crap in the filling tank of a toilet. When someone flushes it later they will get a surprise when the tank fills up with...well you know.
( by the way the filling tank is the big white thing thats behind you when your going number 2, has a lid on it, it's full of water and a few moving parts)
Jake got caught double stacking at wal-mart again!
The act of defficating in the filling tank of a toilet. The next time someone flushes it. They will get a suprise when the toilet refills itself.
Dude! I caught Jake double stacking my toilet again!
When someone sits on the toilet and another person sits on their lap to shit and uses their thighs as a seat.
Tony was shitting and Sam needed to as well, so Sam sat on Tony and used double stacking to shit.