The application is directed to an extracorporeal blood processing system capable of using dialysate to prime the system. A plastic molded compact manifold supports molded blood and dialysate fluidic pathways along with relevant sensors, valves and pumps. The compact manifold is also disposable in one embodiment and can be detachably installed in the dialysis machine. A two-way valve in the manifold is used to direct the dialysate flow through the blood circuit to prime the circuit for use in treatment.
