A car gets "fish tanked" when some idiot leaves their sunroof open during a terrential downpour. The best form of the "fish tank" is when water flows out your door when you open it.
(verb) to bend a girl over a fish tank whilst delivering anal sex to her. Mid-motion remove the lid of the tank and repeatdley dip the girl's head in and out of the tank all the while still ramming the girl in the anus.