We have a 25 gallon water bladder. We used the "Winterize" valve setting to suck water from the bladder, through the winterize port out the shower cold tap then into city water fill port and into the freshwater tank. Picture of the water bladder on the back of the truck.
If doing it this way put the water bladder on the roof of the truck, better gravity flow.
It takes a while to do it this way.
Later I bought a spare pump and use that to pump it into the city water fill port. Much faster to fill the tank. This way the water bladder goes in the bed of the truck.
One of our members made a kit
Freshwater fill kit
https://www.montanaowners.com/forums...ad.php?t=86368
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. The bucket must be level to or higher than the winterizing port. Turn winterize valve to "ON". Connect the outdoor 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 the freshwater tank.