Though I can not help you with the aqua Hot (I'm sure someone else can)
The manual is "Generic" if you had a dometic or surburan gas/electric water heater there would be a drain plug (I know where those are) but I don't know the aqua hot.
When Winterizing there are multiple methods
Some folks pump a pink liquid through the lines and have fun come spring getting rid of it. I did that first year. never again,
After that I took an air compressor and blew the lines out (All valves including low point drains open) forced cycled the ice maker (actually I pulled the solenoid to inside the house) blew again like 10 times waiting a few mintues between blows.. This should blow out your aqua hot.
Finally we got rid of the house and then we winterized by the best method the "S" method.. now we did not use the full "S" method but .
Strap a snow blower to the front of the Motor home or tow vehicle (We did not do this part)
Drive south.
When someone looks. pushes their hat back, Scratches their head and asks "What the @#$@ is that thing?" you are winterized (for us that was Oconee County South Carolina)