Most AG pumps are not self-priming, but are "flooded suction". Essentially this means that you have to make sure there is NO air in the suction line coming to the pump. It's possible to do this, if you have valves on the lines and can 'hold your mouth right'. But it's a serious PITA.

I'd just go to General Tool and get a $40 sump pump and use that.

. . . membership upgraded.