Hum. Assuming the pickup connection is at the top of the tank, then maybe remove the hose from the fitting and cut an inch off the hose. Add some water
to the hose as the pump
could be air bound. Not Likely with a positive displacement
pump but worth a check.
Also check the hose connection at the pump suction and that the pump is not too far above the tank (or the tank bottom), Most have a limit of suction lift
of 5 feet or so. Also that the suction hose is pretty straight and not kinked, no high loops. reinstall the hose and tighten the hose clamp with a wrench, but not too much...
Open a faucet and turn the pump on to get the air out of the system. When the air is gone, close the faucet..