A pressure-driven metered treating chemistry dispensing pump for a laundry treating appliance having a housing having first, second and third chambers, with the first and second chambers each in fluid communication with the third chamber; a fluid inlet fluidly coupling a first fluid to the first chamber; an outlet fluidly coupled to the third chamber; a piston disposed in the housing; wherein, when the piston moves in a first direction in response to the first fluid entering the first chamber via the fluid inlet, the second chamber decreases in volume thereby ejecting at least some of the second fluid from the second chamber into the third chamber, and when the piston moves in a second direction, different from the first direction, the first chamber decreases in volume thereby ejecting at least some of the first fluid from the first chamber into the third chamber to mix the at least some of the first fluid and the at least some of the second fluid to form a mixture in the third chamber, which can be emitted through the outlet.