If you have access to an auto store and a Lowes, you can get a big funnel and some clear neoprene tubing. Sanitize both and insert tube and pour into funnel. I have a couple funnels that I use that will hold a gallon of water, ie: big funnels.
OR you could use a hand type transfer pump, properly sanitized of course. Such as this one.
In the long term, if you have a generator, you could use a small utility pump, an emergency sump pump to be specific. as I have stated in other threads, that is what I use to pump antifreeze through the trailer, via the city water port, but you also could simply run it into the fresh water fill port also.
I take ours and stick it in a bucket of sodium dichlor (pure chlorine, no additives like household bleach has) and let it recirculate for a little while to sanitize it. It will heat the water up hot so only run it a short time. then as long as you keep it sanitized you will be good to go. Simply fill a sanitized bucket with water and pump it in.