Abstract: A dispensing system is provided for being sealingly disposed with respect to, and dispensing a product from, a discharge opening of a container wherein an annular mounting flange extends radially inwardly adjacent the opening. The valve is molded from a material to define a flexible, resilient structure having a head portion and a surrounding marginal portion. The head portion has a normally closed dispensing orifice which opens when the pressure in the interior of the container exceeds the pressure on the exterior of the valve by a predetermined amount. The marginal portion is connected with the head portion and has a generally annular wall defining a generally annular groove which is open radially outwardly for receiving the mounting flange. The annular wall is sufficiently flexible to elastically deform as the wall is forced against the mounting flange to accommodate sealing of the mounting flange in the groove.