A valve system for use in a system including a first source of a first pressurized fluid and a second source of a second pressurized fluid includes a valve housing including a first inlet port adapted to be placed in fluid connection with the first source, a second inlet port adapted to be placed in fluid connection with the second source and an outlet port. The valve system further includes a backflow prevention system to prevent flow of the first pressurized fluid through the second inlet and to prevent flow of the second pressurized fluid through the first inlet port. The valve system is adapted to provide a fluid path between at least the first inlet port and the outlet port to enable fluid to be drawn from the outlet port to the first inlet port. Several of the valve systems of the present invention provide for flow from the first inlet port to the outlet port and concurrent flow from the second inlet port to the outlet port.