Paccar water seperator

[Bigcam3cummins]

My understanding is the filter should be full, fuel gets sucked from the top so if it the fuel is down in the bowl would it not be sucking some air... Could it be the check valve by the primer pump? If it was the priming pump itself is it not support to run for so many seconds and shut off the check valve will close allowing the gear pump to bypass the primer pump.