Maybe this shot will illustrate it better.
The smoked hose is from the top-off tank. It starts from the top right of the image. (In behind the PVC inlet supply from the display tank). That's the float valve at the bottom left of the image. That annoying hose right in the way of seeing the hose/float valve connection is the return to the display tank.
The float valve is non electric. Basically, when the float is up it seals the opening.
Cheers,