A manual pump dispenser includes a plunger head reciprocable between pressure and return strokes, and a pump body having an inlet valve for inletting of liquid product during each of the return strokes. A discharge valve assembly is fitted to a spout for permitting selective outletting of liquid product through the spout during each of the pressure strokes. The spout includes a bore having a predetermined diameter, with a unitary valve disposed substantially within the bore. The unitary valve is made of a material for permitting predetermined axial, or axial and radial expansion thereof under pressure from liquid product during each of the pressure strokes for thereby allowing liquid product to be discharged through a slitted opening in the unitary valve, and enabling rapid contraction thereof against a valve seat to prevent liquid product from being discharged through the slitted opening.