If the pump is bellow the tank, and bellow the
water level in the tank, you might also need to bleed air out of the line to get water to the pump. The ability to do that depends on the type of pump. If it allows water to pass by it, just opening a valve will do it. If not you will need a valve at the pump intake to accomplish it.
If the tank is not above the pump, and the fill port is, run water into the fill until it over flows and then run the pump while it is overflowing.