I have two on my boat. The main is an automatic 750gph pump that if needed I can control via a standard push/pull switch on the dash. The back-up is a manually operated 500 gph unit that is also controlled via a standard push/pull switch on the dash. The automatic has power running to it at all times as long as the battery is connected. I have two 3/4" water dumps located at the rear of the boat. As HaulsBalls stated, a 500gph unit w/ a 3/4'' hose moves plenty of water.