A vacuum assisted priming system for a fluid pump including a housing defining a hopper that communicates with a pump inlet. The housing mounts a first port that communicates with the source of vacuum and a second port that communicates with atmosphere. A check valve allows atmospheric air to flow into the housing under certain operating conditions but inhibits reverse flow. A valve member pivotally mounted within a valve chamber carries first and second sealing elements that are engageable with first and second seats. The lever arm is operatively connected to a float via a lost motion connection. When the fluid level in the hopper rises to a predetermined level, an actuating rod moves the lever arm to a first sealing position. When the fluid level falls to a predetermined level, the actuating rod moves the lever arm to a second sealing position. A baffle located at an inlet to the hopper reduces surging and turbulence in the hopper and defines a circuitous path through which the fluid must flow in order to enter the hopper.