Ugly but fairly simple. Many, many years of trouble free operation. A variation of the mechanical float valve, gravity feed method. I don't have sump or room to mount a container above my display, so use a glass carboy pressurized by an air pump on a timer to feed a mechanical float valve in the display. I shortened the valve by a couple of chambers to reduce the footprint in the tank. I think after 5 or 6 years, I may finally need to replace the float valve. The rubber seal that closes the opening in the feed line when the valve is up has finally hardened to the point where it no longer provides a complete seal. Should be about $10 at the local hardware store.
What I find good about this set up is that everything happens rather slowly & even if something goes wrong, there's generally no disaster in the form of a flood. The fresh water is limited to the 7 gallons in the carboy and the air pump keeps just enough air pressure in there to feed the tank with a trickle when the level drops to open the mechanical valve. It gives me about 7 days of ATO.
