Now that that question’s been more or less answered, what about the verb “to tank”?
At a guess it’s derived from the expression “to tank up.” As in, fill your tank, be it a fish tank, water tank, fuel tank, etc. Or, colloquially, your stomach. So eating and drinking to your fill can also be called “tankin’ up.” Or, for the time impaired, “to tank.”
Just don’t fill your Tank; the mechanicals would probably fare okay, but the electronics, while fairly waterproof, were never meant for total immersion for any period of time.
It’s a land combat vehicle, not a friggin’ submarine.
Of course, in Everquest, “to tank” is to assume the role of a tank, e.g. an armored warrior whose job it is to fight at the front lines and dish out and receive the most danage. Of course, the term “tank” comes from, well, tanks.
So, a tank tanks. Others can tank if they want, but they don’t tank nearly as well as a tank. When someway says “gp looking 4 tank” they want someone to tank who’s really a tank.
But then you can, in real life, tank in the sense of failing miserably. The New York Yankees really tanked in the ALCS against the Red Sox. It was, indeed, a tanking of historical levels of tankosity. So, they tanked too, but they did not tank the way a tank tanks; they just tanked the way you tank if you’re just someone who tanked.
You missed a pun opportunity.
[in advance] You’re welcome. 
The Random House Word Maven on “To Tank”
He does not make an explicit connection, but I always figured that it came from going “into the tank” as in a carnival dunk tank.
(And NoClueBoy, a million.)