How I fill my tank using a bladder.
Takes some simple parts from Home Depot etc.
Two ways to do this with onboard equipment.
Hook your bladder or tank up to the inlet.
Switch the intake to sanitize. This will use the pump to pull water from the inlet instead of the tank.
Using something like Sharkbite or PEX slip on connectors connect your cold water low point drain to your fresh water tank drain. They are both within a foot of each other under the trailer.
A hose and two clamps will work as well.
Open both valves, fill tank.
On my list of things to do is to plumb this internally with a pair of PEX Tees and a 1/4 turn valve between those two lines behind the water compartment.
2019 DRV MS 39DBRS3