When you remove the upper lid of the toilet and shit in the tank.

v. The leaving of fecal matter in the tank of ones toilet, turning the water brown. Primarily done as revenge or a drunken practical joke, but sometimes in an emergency when the bowl is clogged.

n. The shit that is left in tank during such an act.

When you drop a duece in the tank instead of the bowl.

When you take the top off a toilet and shit in it so and replace it so when the next victim flushe's instead of becoming clean it fill's up with shit..

Where you go to someone's house, shit in the tank part of the toilet. the shit in there starts rotting, and starts smelling up the bathroom, and people don't know where the smell is coming from because they never look in the tank part of the toilet.

The act of excreating a log of fecal matter in upper deck tank of a toilet.
Usually as a prank or in desperate need if the toilet is plugged or dirty.

depositing your fecal matter in the tank of an adversary or foe.