Conservation Commode II

See first the link below, Conservation Commode. The idea here is to save water by using the toilet flush to purge the hot water line of previously hot (cold) water, and then use the hot water to wash one's hands. After much thinking about this, I've decided that maybe a simple thermostatic valve in the water line would be more practical. Two handles on a toilet would only be confusing If the water at the toilet was already hot and the wrong handle used, hot water is wasted. New idea is a thermostatic valve, which uses a wax-pellet thermostat to close (vice open as in an automotive 'stat) at about 70-90F. Previously hot water will flow through the thermostat until it closes, and the resultant pressure drop will allow cold water to continue to fill the toilet though an unequal-area check valve. This thermostatic valve device is best placed at a point where both sink and shower can tee off of the hot water line, with shortness-of-line preference going to the sink. I would much like to build this device. If you know of a mechanical thermostatic valve that closes somewhere in the range of 70-100F please link it here. Thank you.