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A peritoneal dialysis system includes a dialysis machine including a pump chamber and a pump actuator moveable within the pump chamber; a pumping cassette including a rigid portion defining a pump well and a flexible membrane covering the pump well; and wherein the dialysis machine is configured to

A peritoneal dialysis system includes a dialysis machine including a pump chamber and a pump actuator moveable within the pump chamber; a pumping cassette including a rigid portion defining a pump well and a flexible membrane covering the pump well; and wherein the dialysis machine is configured to be mated with the pumping cassette so as to hold a vacuum between the pump chamber and the flexible membrane, the vacuum operable to cause the flexible membrane to follow the pump actuator as the actuator is retracted from the pump well of the rigid portion, the pump actuator operable to cause the flexible membrane to move into the pump well as the actuator is moved into the pump well.

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1. A peritoneal dialysis system comprising: a peritoneal dialysis machine including a vacuum source pneumatically connected to a vacuum chamber constructed and arranged to hold a vacuum, the peritoneal dialysis machine further including a stepper motor, and a piston having a piston head, at least a

1. A peritoneal dialysis system comprising: a peritoneal dialysis machine including a vacuum source pneumatically connected to a vacuum chamber constructed and arranged to hold a vacuum, the peritoneal dialysis machine further including a stepper motor, and a piston having a piston head, at least a portion of the piston head moveable within the vacuum chamber;a pumping cassette including a rigid portion defining a pump well and a flexible membrane covering the pump well; andwherein the peritoneal dialysis machine is configured to be mated with the pumping cassette so as to apply the vacuum to a portion of the flexible membrane corresponding to the vacuum chamber, the flexible membrane following the piston head as the piston head is retracted from the pump well of the rigid portion, the piston head operable to cause the flexible membrane to move at least partially into the pump well as the piston head is moved at least partially into the pump well. 2. The peritoneal dialysis system of claim 1, the piston head operable to draw dialysate into the pump well of the pumping cassette as the flexible membrane is retracted from the pump well. 3. The peritoneal dialysis system of claim 1, the piston head operable to push dialysate out of the pump well as the flexible membrane is moved into the pump well. 4. The peritoneal dialysis system of claim 1, wherein the piston head contacts the flexible membrane of the pumping cassette directly. 5. The peritoneal dialysis system of claim 1, wherein the piston head is configured to retract completely out of the pump well, the vacuum pulling the membrane away from the rigid portion of the pumping cassette. 6. The peritoneal dialysis system of claim 1, wherein the piston also includes a piston shaft, the piston shaft in communication with the stepper motor and the piston head. 7. The peritoneal dialysis system of claim 1, wherein the stepper motor is one of: (i) a rotary stepper motor; and (ii) a linear stepper motor. 8. The peritoneal dialysis system of claim 6, wherein the vacuum chamber includes a shaft opening and a seal between the piston shaft and the shaft opening, the seal aiding in holding the vacuum. 9. The peritoneal dialysis system of claim 1, wherein the pumping cassette, when coupled to the peritoneal dialysis machine, is held at a non-vertical angle. 10. A peritoneal dialysis system comprising: a peritoneal dialysis machine including a vacuum source and first and second vacuum chambers constructed and arranged to hold a vacuum, the first and second vacuum chambers pneumatically connected to the vacuum source, the peritoneal dialysis machine further including first and second pistons driven by first and second stepper motors, respectively, each piston having a piston head moveable within the first and second vacuum chambers, respectively;a pumping cassette including a rigid portion defining first and second pump wells and a flexible membrane covering the pump wells; andthe peritoneal dialysis machine configured to be mated with the pumping cassette so as to apply the vacuum to a portion of the flexible membrane corresponding to the first vacuum chamber and to a portion of the flexible membrane corresponding to the second vacuum chamber, the vacuum operable to cause the flexible membrane to follow the first and second piston heads as either piston head is moved by its respective first or second stepper motor in a first direction to fill the respective pump well, the first and second piston heads operable to cause the flexible membrane to move at least partially into the first and second pump wells, respectively, of the rigid portion as the respective piston head is moved in a second direction to empty the respective pump well. 11. The peritoneal dialysis system of claim 10, which is configured to move the first piston head in the first direction to fill the first pump well while moving the second piston head in the second direction to empty the second pump well. 12. The peritoneal dialysis system of claim 10, wherein the first and second vacuum chambers are formed in a housing, the housing including a surface positioned to abut the pumping cassette. 13. The peritoneal dialysis system of claim 10, wherein the first and second vacuum chambers include first and second piston openings for the first and second pistons, respectively, the first and second vacuum chambers further including first and second seals positioned between the first and second piston openings and the first and second pistons, respectively, the seals aiding in holding the vacuum at the first and second pump chambers. 14. The peritoneal dialysis system of claim 10, wherein the vacuum, in the first direction to fill the respective pump well, pulls the flexible membrane away from the rigid portion of the pumping cassette. 15. A peritoneal dialysis system comprising: a peritoneal dialysis machine including a vacuum source and a vacuum chamber pneumatically connected to the vacuum source;a pumping cassette including a rigid portion forming a pump well and a flexible membrane covering the pump well, the peritoneal dialysis machine configured such that the vacuum chamber and the pump well are mated when the disposable cassette is loaded into the dialysis machine;a piston operatively coupled to a stepper motor and having a piston shaft and a piston head, the piston head configured to move the flexible membrane into the pump well of the pumping cassette; andwherein the vacuum chamber is constructed and arranged to hold a vacuum and the vacuum chamber includes at least one wall constructed and arranged to accommodate at least a portion of the piston head such that the vacuum formed in the vacuum chamber pneumatically pulls the flexible membrane to the piston head. 16. A peritoneal dialysis system comprising: a peritoneal dialysis machine including a vacuum source and a vacuum chamber pneumatically connected to the vacuum source, a piston having a piston head, and a stepper motor;a disposable cassette including a hard side, part of which forms a pump well, and a soft side, part of which corresponds to the pump well, the pump well configured to receive at least a portion of the piston head; andthe vacuum chamber constructed and arranged to (i) accommodate at least a portion of the piston head and (ii) contain a vacuum to pull the soft side of the disposable cassette to the piston head to at least partially mate the soft side of the disposable cassette with the piston head,wherein the peritoneal dialysis machine is configured to push a dialysis fluid from the pump well as the piston head and soft side of the disposable cassette extend at least partially into the pump well, anddraw dialysis fluid into the pump well as the piston head retracts from the pump well and the vacuum holds the soft side of the disposable cassette in at least partial contact with the piston head. 17. The peritoneal dialysis system of claim 16, wherein the piston head is configured to retract completely out of the pump well, the piston head and vacuum causing the soft side of the disposable cassette to move away from the hard side of the disposable cassette. 18. The peritoneal dialysis system of claim 16, wherein the stepper motor is one of: (i) a rotary stepper motor; and (ii) a linear stepper motor. 19. The peritoneal dialysis system of claim 16, wherein the disposable cassette, when coupled to the peritoneal dialysis machine, is held at a non-vertical angle. 20. The peritoneal dialysis machine of claim 16, wherein the piston head is shaped and sized similarly to the fluid-contacting surface of the pump well of the cassette. 21. The peritoneal dialysis system of claim 15, wherein the vacuum chamber accommodates at least the portion of the piston head via an aperture in the at least one wall to allow the piston shaft to move back and forth sealingly within the aperture. 22. The peritoneal dialysis system of claim 16, wherein the vacuum chamber includes a wall located between the piston head and the stepper motor to accommodate at least the portion of the piston head.