Anyone interested in 83 Pace Arrow Tear down and Rebuild?

I have 2 questions for anyone who knows more about this than I do.

1. If I divert the urine from the toilet to the gray tank, is that still considered ... gray tank? Black tank, would only have to be black only, with water, of course, correct?

2. Does anyone know of a 120 volt ac inline water heater, that is able to control the temperature of the water by adjusting the voltage to attain the correct output temperature? I don't want to just use a mixer to add cold water to get the correct temp.

Thanks.