fresh water pump runs but won't prime and push water

We had a case recently, where the pickup for the pump, and the tank drain valve, were installed at the same port in the bottom of the tank. The Valve had a slight leak, dripping water out of the tank. But when the Pump ran, it pulled air into its suction and wouldn't prime. Water in the tank just lies there, but the pump has to develop suction and pressure, so a small water drip could be a big air leak.