The aqua hot unit has 2 systems in the one unit. One system is for the heating of the coach, and has permanent antifreeze in it, and requires no winterization. The other section is the domestic hot water system, and needs to be winterized. This can be done with blowing out with compressed air, through all the hot water fixtures, one at a time. I always take extra cautions and are very thourogh with this process, taking a lot of time, blowing lots of air, and repeating every fixture.. The aquahot does not have a separate tank, like a gas fired hot water tank is. It is an internal loop of coiled copper wire, that is immersed in the hot coolant for the heating section. Need to blow lots of air through this coil to be sure that no water is left trapped in the lower sections of the coil. You may not want to hear this, but, I follow up with rv antifreeze after blowing out with air, for additional protection. My coach has a separate tank to put the antifreeze into, and uses the water pump to pump the stuff through all the pipes. If you don't have this, you can buy a fitting that hooks to the water pump, with a short section of hose, that you can put in the gallon jugs, and pump the stuff through the pipes, I run it until I have pink stuff at every fixture. I do not put the pink stuff in the water tank. I also do not run pink stuff through the ice maker on the ref. Remember to run enough pink stuff, so every trap has some, and so the waste valves, black and grey have some.