I assume you have seen or own the air fitting that will connect to you city water fill line. If not you will need to purchase one. Almost all RV stores will carry them. Obviously you will need and air compressor capable of generating 40 psi.
Worldwide Merchandise Company - Blow Out Hose - Winterizing - Camping World
Camco Mfg Inc - Blow-out Plug - Winterizing - Camping World
There is a brass version of this plug which I use just couldn't find the link. I also have the version that will allow you to attach a 1/4" NPT female air fitting. The one shown will allow to use a regular tire inflator tip, maybe more common around the home garage.
Here is my basic procedure for using air pressure vs. anti-freeze. This is for a Safari Cheetah. Your coach may be somewhat different. Hopefully this gives you some ideas.
I still pour a bit of anti-freeze in the P-traps and tanks to protect the tanks valves.
Your owners manual should have a winterization procedure in it.
Note the steps below do not cover additional appliances like washer/dryer combos, ice makers etc.... The OEM manuals for those appliances should have winterization details in them.
Using Air Pressure
1 Access to an air compressor and an adapter to connect the air line regulator to the water system is necessary. Air adapters used for winterization are available at RV supply locations. Air pressure should not exceed 40 PSI. Higher pressure can damage the lines.
2 Empty and flush the holding tanks.
3 Disconnect the water line connections on either side of the water filter bowl head. Connect the bypass hose to the water lines. Unscrew filter bowl, remove old cartridge and empty any remaining water in the bowl. DO NOT screw filter bowl back onto filter head (see “Water Filter”). the water lines.
4 Drain the fresh water tank by opening the fresh water tank drain valve and the fresh water tank low point drain. Open the water pump shut-off valve. All are located in the roadside water service center.
5 Open hot and cold water low-point drains. Open secondary ice maker low point drain valve (if equipped). All are located in the roadside water service center. Leave low point drains open until the motorhome is used again.
6 Add in OEM instructions for various appliances like washers, ice makers, etc...here
7 Turn the water pump on for 30 - 60 seconds and allow it to run so that all the water is cleared out of the pump and water tank.
8 Turn the pump off.
9 Close fresh water tank low point drain valve, water pump shut-off valve, hot and cold water low point drains and secondary ice maker low point drain.
10 Leave open fresh water tank drain valve and secondary ice maker shut-off valve.
11 Open the water heater exterior access door. Open the high temperature/ pressure relief valve to vent water heater. Remove water heater drain plug to allow water heater to drain. When water has finished draining, replace water heater drain plug and close pressure relief valve.
12 Locate bypass valve at back of the water heater and move valve to BYPASS position.
13 Connect an air hose with regulator to the City/Fresh Water Fill connection. Position the City/Fresh Water Control lever to the “City Water” position. Set regulator to 40 PSI and turn on air compressor. Do not exceed 40 PSI in the water lines and faucets.
14 When water stops flowing from low point drain valves, open all faucets - including outside faucet and shower, one at a time, until air comes out. Do not forget to drain the shower faucet.
15 Hold toilet mechanism open until the water has stopped running.
16 Shut off the air compressor and disconnect the air hose.
17 One gallon of FDA approved RV antifreeze is needed to protect various water drain lines in the motorhome. Pour 1 pint into both the kitchen and bath shower drains. Pour 2 pints into the bath sink drain. This will protect the P-traps with some of the antifreeze going into grey tank to protect the drain valve. Open the toilet bowl valve. Pour another 3 pints into the toilet, letting the antifreeze run into the black tank to protect the valve located there. If applicable, pour the last pint of antifreeze into the washer/dryer drain after the toilet bowl valve has been closed.
18 Use a soft cloth to wipe out the sinks and shower (after the antifreeze is poured in) to protect the surfaces from stains.
19 Leave the low-point drains open until the motorhome is used again.
20 WARNING When draining the low point water drain lines and the water heater be sure the water is not hot. Hot water from the lines can burn or injure skin.
If you have a friendly service guy ask him to walk you through the process the first year.