There is provided a tank including: first and second chambers; a liquid inlet port; a first communicating port; a communicating channel; a second communicating port; an atmosphere open port; a gas-liquid separating membrane provided in the communicating channel; and a liquid outflow port. In a state that a first wall constructing a first end of the tank in a usable posture constructs an upper portion of the tank and that a second wall constructing a second end, of the tank in the usable posture, which is away in a horizontal direction from the first end constructs a lower portion of the tank and under a condition that a maximum amount, of the liquid, storable in the tank in the usable posture, is stored in the first and second chambers, the gas-liquid separating membrane is located at a position above the liquid surface of the maximum amount of the liquid.