the bottom float switch sends water to the sump, the top float switch is a shut off switch in case the bottom one gets stuck.
the float switches are hooked to two soleniods which when open let in ro/di water from the filter directley. I have a four gallon holding tank for the RO water. when the float switch's activate the tank pressure sends water through the DI filter and goes into the sump.
This is the best thing I have done for the tank, and my apartment.
I have no large resevior sitting in the living room, and the tank is always getting fresh RO/DI water