A rotary valve, a piston pump rotary valve assembly and a piston pump rotary valve assembly tank dispenser for use in discharging a metered amount of liquid, gel, or slurry has a valve body having a first channel pathway and a second channel pathway. The first channel pathway has an inlet opening to receive a liquid, gel, or slurry and an outlet opening to provide the same to a pathway of the piston pump assembly. The second channel pathway is segregated from the first channel pathway and includes a plurality of inlet openings, each capable of communicative alignment with the pathway of the piston pump assembly, and at least one outlet opening communicative with such inlet openings. The valve body is capable of rotation with respect to the piston pump assembly to dispose both the first channel pathway and the second channel pathway each to two operative positions to receive the liquid, gel, or slurry and to two inoperative positions blocking fluid communication with the liquid, gel, or slurry.