120 AC volt water transfer pump from Lowe's Home Improvement.
35 gallon water tank and spigot attached (bought separate) from Tractor Supply Company (TSC).
I have a 400 Watt inverter I keep in the truck all the time in the event I do not have AC electricity. Both AC 120 and DC 12 volt (battery) with the inverter work the pump quite satisfactory. I've been doing it this way for several years now. I am on my 2nd pump now.
It works well for filling a gravity fill water port, or the garden hose attachment-flip the valve to "fill" hook up.
(Just an FYI, I tried using my on-board water pump, even the winterizing port directly from a water container. I could never figure out a way to get the on-board to pull water from anywhere except the fresh water tank or the winterizing hook up.)
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2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually