Most all diaphragm pumps have a one way valve on the inlet and outlet, so the flow can only go in one direction. In fact, if the motor will run in reverse, the pump would still flow in the same direction.
Edit: Don't back pressure through the pump as it will likely damage the valves.
I'm tired of fast moves, I've got a slow groove, on my mind.....
I want to spend some time, Not come and go in a heated rush.....
by The Pointer Sisters