Danger, just because the gauge says the tanks are empty, does not mean there may not be a small amount of residual water left in it, enough to do damage. Open the valves and let them drain. Drain the hot water tank, the fresh water tank, and the two holding tanks. To drain the hot water tank, probably have to remove the electrical heater anode, open the pressure relief valve so it drains completely. Then close all those on the water heater, and look for the hot water tank bypass. Usually on the inside near the hot water tank.
Go to Walmart, Lowes etc and by RV antifreeze, it will be pink in color. I buy 4 gallons( more than I need, if you go cheap, and miss something and it freezes and breaks, it will cost a lot more to,repair than a $ 5 gallon of anti freeze).
Pour or pump, all but 2/3 of a,gallon into your drinking water tank. With the pump on, turn on the kitchen faucet, and let it run until it is pink in color. Do each faucet kitchen, bathroom, shower sink, toilet. Couple words of caution. The 2/3"gallon you did not pour into the tank....pour a,little in each drain to make sure anti freeze is in the traps. Buddy forgot the shower drain, it burst the next spring and was,a,real pain to repair. My toile has a pedal flush valve and a rinse hose, I forgot to move the pedal up as well as down one year, cost $80 for a new toilet input valve. If you have a hose or outside shower, make sure you run pink stuff thru that, and the shower hose as well as,the shower faucet. Ice maker? Disconnect the input line and make sure you have run pink stuff thru it. Washer? Drain it all hoses, input and drain lime and trap. I then drain the black and grey tanks again, to get the water out that went in there when I started process. Once that is done and closed pour what is left of your antifreeze into the toilet and flush it. Pure antifreeze now in the black tank and at the dump valve
2007 Newmar KSDP. 3912
2010 Nissan Frontier SE