look up any word, like the eiffel tower:
 
1.
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!
by M. Weazel January 29, 2006
 
2.
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!
by M. Weazel January 30, 2006
 
3.
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.
by shit-bag October 12, 2010