I too have used the winterizing hose connection to draw water from a five gallon bucket or a 7 gallon aqua tainer.
The aquatainer spigot screws into the bottom of the aquatainer cap for storage and screws into the top of the cap to use for dispensing water. The thread is 3/4 inch npt as is most plastic spigots that screw into the Caps of similar jugs.
I have a spare aquatainer cap that I screwed a plastic three-quarter inch male npt x hose barb fitting into to replace the spigot. I can slip the winterizing hose over the barb and turn the jug on its side and draw water through the pump from the jug when the fresh water tank goes empty.
In an emergency I can use an aqua tainer or any other jug or bucket as an emergency water supply. I also use the cap with the hose barb when I sanitize. I can fill an aqua tainer with two gallons of water along with the proper amount of bleach, attach a piece of tubing to the Barb, fish it down the freshwater tank water fill port pouring the contents in and then top off the tank.
The tank is under the trailer and supported by the frame along with an additional piece of angle supporting the middle of the tank. There is insulation and a piece of coroplast covering the bottom of the tank. It does well for the temperatures here in Virginia but every 10 years or so we do get single-digit temperatures overnight and teens in the day.
We had a few days of such temperatures and the water fresh water tank began icing up enough to block the tank suction tube. I had to use the 7 gallon aqua tainers for a couple of days until the temperatures warmed up enough to allow water to flow from the freshwater tank again.