Depending on the features of your coach, there are many steps to winterizing.
Does your coach have any water filters? Does you coach's refrigerator have an ice maker or washing machine?
Basically, you want to remove all of the water from the systems. The gray and black water tanks should be drained, before you start. The drain for the fresh water tank will do a good job for that. And the drain plug for the water heater should drain it. (I usually open those drains, or plugs and after the water quits draining, I dive to a service station and fill up the fuel tank. The point is to get out any residual water.)
The low point drains for the water lines should not be relied on to eliminate all of the water from the lines.
Hopefully, your coach has a water heater by-pass valve. You don't want to put antifreeze in the water heater tank because it is too hard too flush out in the spring.
And hopefully, your coach has a winterizing valve that allows the water pump to pump antifreeze into the pipes.
That said, here are the steps:
Remove water filtes.
Set the water heater bypass valve to bypass the heater.
Turn the pump valve that allows it to siphon antifreeze to the winterize position.
Put the siphon tube into the antifreeze container and turn the water pump on. (see not below)
Open each hot and cold water faucet one at a time until antifreeze just begins to from the faucet. Don't forget the external shower, if you coach has one.
Press the toilet flush pedal until antifreeze begins to flow. Leave a little antifreeze in the bowl.
Turn off the water pump and turn the winterizing valve back to normal.
Pour a little bit (about a cup) of antifreeze into each drain.
Note: The process of adding antifreeze usually require two people. One outside handling the pump, siphoning tube, and container of antifreeze. Antifreeze comes in one gallon container and one gallon will not be enough. When a container is emptied, the pump must be shut off and the siphoning tube inserted into a new container.
There is one other notable method of winterizing, which involve blowing out the lines with an air compressor, but we will leave that for another discussion.
On edit: I like Dick_B's suggestion.
Tom
2015 Meridian 36M
2006 CR-V toad
3 golden retrievers (Breeze, Jinks, Razz)
1 border collie (Boogie)