A portable peritoneal dialysis apparatus having a side-hinged, inclined door for enclosing a disposable cassette that seals tightly shut using air pressure which imposes a safety interlock, a cassette with its inlet/outlet tube exclusively along the lower edge so that the connected lines can hang straight, a circumferential channel defined in the cassette, and a pneumatic system for sealing the membranes of both the pump chamber diaphragms and the pressure sensor diaphragms in the cassette to the respective mating pistons and pressure sensors in the cycler. In addition a system for draining patient line fluid to an empty solution bag is disclosed.