I use one of these to add water to our rig.
https://www.harborfreight.com/search...20water%20pump
We have a gravity fill outside but also have used it using the water valve in the convenience center turned to fill. I have a 45 gallon bladder, and along with the pump and hoses, can fill the fresh tank.
https://www.campingworld.com/portabl...llon-1605.html