An apparatus for mixing a fluid including a storage vessel including a hollow portion for holding the fluid, the hollow portion including at least one access port, the at least one access port adapted to at least one of receive and expel fluid and a diaphragm pump in fluid communication with and removeably coupled to the vessel, the pump adapted to move fluid into and/or out of the hollow portion. Either the vessel or the pump can be disposable. Also, at least one portion of the vessel can be made of a flexible material that takes shape in relation to the contents of the hollow portion. Also, the fluid can be moved between the vessel and the pump by natural or artificial pressure.