Water Pump Issue

I live in Alaska and bought a used 2017 hour pod 180 this winter. Everything seemed to be in pretty good shape but now that it’s above freezing I am trying to get ready for the camping world. Using house power I flushed out the plumbing pipes. Now I fill up the freshwater tank and turn on the pump which runs continuously and with all the faucets open, I hear a bunch of air and just a little bit of gurgling. Filling the plumbing up with water it seems to pump it out very well, but when the pipes are empty, it still has not primed. Searching online there appears to be very little to no information on the various systems. Before I start tearing things apart is there a good source of information on the 12 V water pump and its method of operation? at 40°F I would like to stay dry as I attempt to fix this problem. I do have the generic Forest River travel trailer owners manual, which appears to be very lacking in almost all aspects.