An embodiment of a peritoneal dialysis system includes a peritoneal dialysis hardware unit having a housing with a first opening, a door coupled to the housing and having a second opening, and a solid pump piston having a solid piston shaft attached to or integrally formed with a solid piston head. The system also includes a stepper motor operable to cause the solid pump piston to translate; a disposable pumping unit having a first and a second opposing surface, and a fluid pump receptacle extending from the first and second surface to fit within the second opening. The hardware unit and pumping unit are structured and arranged to allow the pumping unit to be placed into the hardware unit such that the fluid pump receptacle is aligned with the first opening, the second opening, and the solid piston head when the door is closed against the housing.