Remove drain plug from WH, and open release valve on spring to then drain.
Turn all 3 bypass valves to - from WH to closed position. Thereby isolating WH from needing RV Antifreeze.
Open ALL floor valves located along and through coach, including main water tank valve.
Once all water drained by gravity, close all floor valves.
Buy one gallon on RV Antifreeze (pink) liquid from Walmart Supercenter.
Open top screw valve on water pump. Attach clear 3' hose provided by RV manufacturer to water pump, with open end of hose into the open gallon of RV Antifreeze.
Turn on water pump and let it distribute RV Antifreeze to all points until it stops running. Then go to and open one water faucet at a time in interior of coach. When pink fluid comes out, close that faucet, going to the next faucet. Open commode valve with foot pedal until pink fluid comes out, then release. Leave some pink fluid in the commode bowl to keep O-ring that holds water stay pliable. Commodes (most of them...) also have a rinse-hose on their assembly. Be sure to let the pink antifreeze run through it too.
Your small coach' s plumbing is now set.
Replace water hose coupling at water pump.
Now, pour a few ounces of pink fluid in all 3 other drain traps to protect them too. Galley sink / shower drain / lavatory sink.
If the coach has an exterior shower faucet- let pink fluid run there too before then closing valve.
You may need to buy 2 gallons your first time through. Price should be $3.99 +/- a gallon @ Walmart. The cheapest I've found, BTW.
You're now good to -50F. Pink fluid will thicken, but not burst piping. RV Antifreeze is non-toxic, and rinses easily when flushing the system next Spring.

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'06 E320 CDI
'17 Corvette Stingray Vert