Since this old post still seems to get a fair amount of inbound linkage, I figured I’d help to clarify the origin of the common expression “in the tank”—as in “the media sure are in the tank for Obama/McCain this year!”
The original “tank” here is a water tank, which also used to be a slangy term for a swimming pool. From there we go to old sporting slang, where a boxer who “takes a dive” in a fixed fight might be described as “going in the tank” or “tanking”—deliberately hitting the mat as though he were diving into a swimming pool. And from there, the transition to the current usage should be pretty obvious: The media are supposed to be neutral and skeptical, but the claim that they’re “in the tank” is to suggest that they’re participating in a rigged contest.
And there you have it.