Johnson 12V 1000 GPH Multi Port Shower Pump with Switch 12V 1000GPH Multi-Port Grey Water System For showers, dish-washing machines, galley sinks, etc. The shower sump turns on/off automatically using Ultima switch. The check valve on the outlet stops water from flowing back into the tank. The shower sump turns on/off automatically using Ultima switch The check valve on the outlet stops water from flowing back into the tank