A valve for controlling flow of fluid from an inverted fluid reservoir, the valve comprising: retaining mechanism for coupling the valve to a fluid reservoir; a central fluid opening for flow of fluid from the fluid reservoir through the valve; a valve post slidably disposed within the central fluid opening, the valve post having a sealing portion adapted to seal the central fluid opening and prevent fluid flow through the valve in a closed position; a biasing mechanism coupled to the valve post for biasing the sealing portion of the valve post against the central fluid opening when the valve is in the closed position; and an air vent system.