I have a 2017 Citation, but not the tankless WH. Mine has a drain plug, that I open and drain out the water. Manual says that should be sufficient. I don't like getting RV antifreeze in the WH. I use an air compressor attached to the "winterize" fitting in the left rear water bay and blow out all the lines (all sink faucets, etc open). I put a gallon of RV antifreeze in the toilet and flush leaving a little in the bowl. I pour some in each of the sink & shower drains and make sure I get plenty into the grey tank.
I pull the chassis battery disconnect (by the accelerator pedal). I take a picture of the 2 house batteries under the step, then remove them and take them home to keep the warm and charged. (I park my MH 2.5 miles away.)
That's it. We get some January & February temps down into the teens. I haven't had any problems in 3 years.
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