My Roo 19 has 37 gallon tank.
As for water, I put in a valve to fill the tank from the pressure side of the water supply. I hook the fill hose up to a pressure regulator and then to the 'city' water connection and it flows through the onboard filter and through my open valve to the tank. I open the cap to the standard fill port to let the air vent more freely when doing this also. I also open the pressure relief valve on the water heater so that it gets filled while taking on water if it was empty. That way I don't instantly use 6 gallons out of my tank.
If the end of the fill hose is buggered up I can use a water thief, or use the standard fill port and then turn on the pump after a bit and open the pressure valve on the water heater. Of course I don't use my valve for that situation. I prefer to use the water thief if possible so that the water gets filtered before it goes to the tank, to keep junk out of the tank.
Early 2016 Rockwood Roo 19