My camper can not be 'gravity filled'. I bought a exact copy of my water pump and made an adapter for each side of the pump. Bolted it to a short board, with handle and on/off switch. uses only 12 volt. Have two blue water cans from wallyworld. Works really nice. Everything (pump/cord/hoses) is stowed away in its' own 'tool bag' for when I need it.
2013 Forest River Salem Hemisphere SBT312QBUD
2001 CrewCab F-250 7.3 PowerStroke Diesel
SuperChip, BTS transmission, 6.0 Trans Cooler