All these auto-top offs...

[Majestic_Aquariums]

I think the idea is great, and obviously so does everyone else. Feel free to call me stupid here if I am missing something. Why couldn't a person use the same type of float valve as inside of your toilet tank? Not the ones with the big arm and ball. They have WAY too much metal obviously. But, there is a type called FluidMaster. Take up way less space, are adjustable, and are 99% pvc, other than one stainless spring.
You would howver have to supply the sump from the side, and have your water elbow upwards into the unit.
I think they are under $20 bucks @ Home Depot
Would this not work? Lemme know what you think.