Cleaning a Thermoquad. What can I use, and what should I definately not use?

I know my son turns the heater on an hour or two before using. The timer for the unit is 20 mins. rinse with water immediately afterward the cleaner is caustic. I will find out from him excactly where he gets the cleaner. I asked him one day about adding cleaner and I remember him saying its a special Super Clean cleaner. It is in a 5 gal white plastic container that he uses.

here are my heads before and the after the cleaner




This was after cleaning







And yes those are all the same parts including the valves