“Wank tank” is a derogatory term for lifted, oversized pickup trucks, implying they’re as big as a tank, but with the only purpose of serving as wank material for the owner.
In these pictures, the pickup truck has a longer wheelbase than the tank, and is overall of comparable size, confirming that the moniker is appropriate.
The bicycle in both pictures with the parallel lines proves that both pictures are at the exact same scale.