There is provided a tank including a casing provided with first and second walls; first and second chambers; an atmosphere open port; a first communicating channel; a second communicating channel; a liquid inlet port; a first communicating port; a second communicating port; a liquid inflow port; and a liquid outflow port. Under a condition that the tank is in a posture in which the first wall constructs an upper portion of the tank and that the second wall constructs a lower portion of the tank in a vertical direction and that a maximum amount, of the liquid, storable in the tank in an usable posture of the tank, is stored in the first and second chambers, the first and second communicating ports are located at a position above a liquid surface of the maximum amount of the liquid.