WHALE Socket Motorhome Fill. Directly fill your on-board water tank with the Onboard Tank Fill Socket. The unique secure hose clip keeps the pump in place during filling. The tank fill design incorporates a lock to protect your water supply and a vent pipe to prevent airlocks. The Onboard Tank Fill Socket is suitable for use with any standard hose and should be used with cold freshwater only. Slick design – uniform look on the vehicle's exterior walls. Comfortable to use. Waterproof protection. High quality satin finish. UV stabilised to prevent damage from sunlight.