The float switch is part of the kit.
The submersible pump is designed to remove surplus water from a collecting tank by pumping it out automatically. The float switch actually tries to float in the water. Once the water gets deep, the float switch will be vertical as it is held by the cable. In this position it will activate the pump and drain the holding tank of water. As the level of water drops the float switch will still float but in a horizontal position which will switch the pump off.
The float switch thus allows the pump to work in the background with little attendance.
We have adapted this pump for window cleaning. You plug the pump into the socket and leave it switched off. Once the IBC tank is full you either manually or automatically switch the r/o off stop production.
When you need to fill the van's tank, put the hose in the tank and switch the pump on at the plug socket. The pump will then run until you switch it off when the tank is full. The float switch will still work if you forgot about the van filling up. Yes the van will be soaked, but when the IBC tank is nearly empty, the sub pump will switch off automatically.