Mmmm I'm interested! Using my DIY float switches (from fleabay) for Airconditioner condensate pump, all OEM sensors kept failing and they cost a lot. I thus made a dual float switch that I connected self holding relay when floats are up, so it stops cycling the pump too much and gives the system hysteresis. Works a treat...except I need a separate or 3rd sensor for Flood. In case the pump fails. Pump is great its just the OEM sensors, Sauermann.
I cannot fit another float in as I'm using 50mm PVC pipe as the reservoir. I mean I could if I re-did it all, put the existing floats on the bottom, swap over connections and floats, install another small float in the top, might squeeze. I'm constrained for room as the reservoir fits between walls. So if I can sneak in another small sensor to existing...winning!