I called the manufacturer. Two ways to do it, either works. Don't touch the bypass valves just run antifreeze through the system. There is a drain on the back of the water heater but the wall is in the way and you can't get to it. That would be the other way. I just run ant-freeze through my system. Has worked for the last two Winters.
2015 Chev Silverado 3500 dually D/A
2016 Cedar Creek 36CK
B&W Patriot 18K, Trail-Aire pinbox,
Level up, dual panes & all that stuff...