To winterize your unit, drain all the water out of the tanks and lines(including shower, toilet, kitchen faucet, outdoor shower, and water heater).
At this point, you can take an air compressor and blow out your water lines, and this would suffice.
*There are air line attachments that will attach to the city fill side to do this process.
You can go the extra mile with winterizing by using anti-freeze.
*NOTE: Make sure your hot water heater is isolated by closing the 2 valves(one on cold water line, one on hot water line) and the bypass valve(valve that connects the hot and cold water line) is open.
You will want to add some anti-freeze to the fresh water tank.
Afterwards, prime your kitchen faucet, outdoor shower, and shower until you get the anti-freeze.
This would complete the winterizing process.