Don't forget to pull the plug/anode rod on the water heater to drain it. I believe you should also have another valve to bypass the water heater. It should say "bypass" and "normal".
1-When you're ready, open all the faucets in the unit,
2-Open the "low point drains (located outside under the unit, this drains the lines in the unit),
3-Drain the water heater, put water heater valve in "bypass" position,
4-Put main valve in "winterize" position (this will allow the suction of RV Antifreeze from jug).
5-Get or make a short length of hose w/male end. Attach it to your normal "city" port. Put the other end of the hose into an open jug of RV Antifreeze.
6-Close all faucets including low point drains.
7-Turn on the onboard water pump.
8-Open the faucets one at a time (both hot and cold) and let run until the RV Antifreeze comes out.
9-Pour enough RV Antifreeze into ALL the drains to displace and remaining water.
10-Don't forget to drain your fresh water tank too!!!
BTW - About 3 gallons should do the job.