A Tank is a BuildCraft block used to store liquids, such as Water, Lava, Fuel, and Oil. One tank block can hold up to 16 buckets of liquid. Tanks placed next to each other will not be connected, however while placed on top of each other, they will link together and function as a single, larger tank.
When filling stacked Tanks with waterproof pipes, they will fill the entire stack, regardless of the pipe's location relative to the top or bottom of the stack.
However, when extracting fluids from a tank using wooden waterproof pipes, the pipe must be on the bottom Tank of the stack.
Tanks are useful when you want to store the fluids. Their large capacity makes them a good container for Oil and Water for Combustion Engines.