I'm looking to supply my toilet tank with rain water and grey water from, say, the washing machine, but if that's not enough water to fill up the tank, I want to use water from the water mains to top it off. Preferably, this would be an automatic solution, so that I can use as much waste water as possible but never end up with an underfilled tank.
I don't have room for a large underground cistern, preferably I'd just modify the toilet's tank so that it takes in the water from both the mains and the waste water directly.
I've been working on a design (some frankensteinian monster involving two valves and float arms but I can't figure out how to get it to use the "waste" valve first and only activate the mains valve when there's no more water coming from the waste valve and the tank isn't filled to capacity yet.
Anyone have a good design for inspiration?