adj. used in refferance to a chick's ass, communicating that the ass is both round and firm and though it may appear to be large, in porportion to the rest of her body it looks damn fine.
"That chick has a tank ass!"
"Which one?"
"That one there with two strange bulldogs pawing at one another in the back of her jeans."
"Oh!... That's a tank ass..."
One who like the infamous "shotgun" call, calls out "tank" to be the one who drives as opposed to the "shotgun" call where they would recieve front passenger seat.
The act of removing a toilet tank lid, standing on the seat, and taking a dump in the tank of a toilet so the next person who uses it flushes out shit.
"Man, they fucking fired me so I tanked that fucking toilet on my way out!"