Using hot water in a toilet can be done as long as the incoming water on the flush is not cold water. Now set back: When water is heated it releases all sediments in the water when it cools the sediment will drop to the bowl of the tank.
Causing a rust look. do u really want the hot water to make your but sweat when you are using the john! and Pay the electric or gas companies to heat your toilet water, and finally when bowl and urian is in heat it produces an awfull stench.