The application is di-rectedto an extracorporeal blood pro-cessingsystem capable of usingdialysate to prime the system. A plas-ticmolded compact manifold supportsmolded blood and dialysate fluidicpathways along with relevant sensors,valves and pumps. The compact man-ifoldis also disposable in one embod-imentand can be detachably installedin the dialysis machine. A two-wayvalve in the manifold is used to directthe dialysate flow through the bloodcircuit to prime the circuit for use intreatment.