De winterizing is simple. Hook up your trailer's city water connection to a pressurized water supply system (using a pressure reducer if necessary) and start turning on the faucets, showers and flush the toilet. Run the water until it runs clear. You may want to open the low point drain valves to help flush the anti freeze out of the system but it seems like I always have residual anti freeze in the system after flushing. Shut the water supply off, then open your water heater bypass valves and open your grey and black tank valves to empty that water out of them.
2017 Ford F250 XLT, 6.2 gasser
2013 26BH (traded)