[scottz]

Originally Posted by Meauwataka

If you don't have any fresh water in the tank that you are hauling with you, but you need the heaters for the grey and black tanks, seems like you'd need to know which ones to turn on or else the heater would be heating an empty tank, which I don't think would be good for the tank or the plastic. Am I right?

I have three switches for the black and two gray tanks. I do not believe there is a heater on the fresh water tank.