well I have that. I read some time ago about someone made and auto top off system with about 1 gal. or 5 gal of water that would put in the correct amount of water as the water in the sump evaporated. You don't know anything about this? I think it worked on the thorey of vacume example
put a glass full of water and turn it over very quickly putting the top edge of the glass in the water and the water will stay in the glass. In the sump it will stay in the glass till the water level lowered.
But Im not sure if that is how it worked or I miss remember what I read.
Well thanks for your help anyways.
If you know what I am talking about let me know.