[Daryles]

You can get antifreeze into the freshwater supply hose by using this same method (you only need to do it for a few seconds though...

Filling freshwater tank using winterizing port.
Take 5 gal bucket of freshwater. Connect a pickup hose to the winterizing port (sometimes you have to use 2 washers to make a good seal). Put the open end into the bucket of water. Turn winterize valve to "ON". Connect the shower hose to city water connection. Turn "Normal flow/Fill" valve to "Fill". Turn water pump on and open cold water side of shower. Water will draw from 5 gal jug go thru shower hose into city water connection right into tank.