I use a Fill line made from a cap off a 5 gallon water tote available at any home store. We use the bottled water for drinking and making coffee.
The empty bottle is used to fill the fresh tank from the potable spigot at the campground.
5 gallon filler mod pictures from travel photos on webshots
I have a foldable tote that I use to wheel the bottle around. 6 trips empty to completely full, but most times I will top off every few days with 3 trips.
Not visible is a small hole in the plastic cap (that goes through the plastic but not the foam seal) for air to enter the bottle to increase flow.
Hose goes into filler; invert bottle.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW