A peritoneal dialysis system includes: (i) an enclosure; (ii) a stepper motor housed by the enclosure; (iii) a pump head in operable communication with the stepper motor; and (iv) a disposable unit including at least one flexible membrane attached to a rigid piece, the enclosure configured to receive the disposable unit such that the stepper motor can move the pump head towards and away from the flexible membrane to cause, (a) the flexible membrane to move outwardly with respect to the rigid piece as the pump head is moved away from the disposable unit, and (b) the flexible membrane to move inwardly with respect to the rigid piece as the pump head is moved away from the disposable unit.