an improved plastic seal valve for the bottom of the chamber of a dispensing device in which a valve stem operates . the valve stem is hollow and contains a cross hole which is normally located just above an annular plastic seal made between the housing and the stem at the bottom of the tank , the cross hole porting the hollow stem , with the plastic seal allowing closer tolerances in manufacture of the stem and allowing greater accommodation for such distortions as may still occur in molding through flexibility in the bottom stem portion the stem having a taper that just release the sealing pressure and functions on the bottom seal as the upper seal closes . in addition a weaker spring may be used , thus , making it easier to operate the valve while at the same time obtaining improved sealing over the life of the valve .