This appears to be a hypothetical device, but unless it has been proven in use, I suspect it is not a good idea. I don't think the thermostat valve will close quickly enough in contact with the cold dirty water to prevent contamination of the clean water tank.
A better -- albeit more complex -- solution would be to use a toilet-tank style flush/fill mechanism. When the tank reaches Pasteurization temperature, it could flush then refill with dirty water again. That way, only Pasteurized water is allowed to enter the clean water tank.
- Devices such as this have been built by people who know how to test whether there is any contamination of the water by processes like you describe. As far as I know, this is a theoretical problem that doesn't occur in the real world. More info on this here and here. Thanks for your input here. Tom Sponheim 16:16, 17 March 2009 (UTC)