I have a in-sump dual switch unit from AutoTopOff.com
Water from my RO
goes into this storage container. The pump in the container is controlled by the ATO. (The float valve on the right, near the top, shuts off the RO
so it doesn't overflow the container. I don't have my RO
on all the time because the unit works best if it runs longer and not just doing a little at a time.)
This is the float switch in the sump. As the bottom switch drops from water evaporation, it turns on the pump in the container and when the water level rises and raises the switch it turns the pump off. The upper switch is only a backup in case the lower switch fails. It's just a safety feature so my sump won't overflow if a switch fails.