Good pic. So we should probably all winterize those and the question returns to how. Those with a compressor can do the air thing and that should work. They just have to remember to go around and do that valve also but a question asked above is how to do it without a compressor.
Would one of those miracle grow things (filled with pink stuff not fertilizer) hooked to a hose do the trick or would it be too diluted?
A related question: Can you do the compressed air with the four way valve? (I know you'd also need to do the flush line connector)
When you blow out the lines, you connect the air at the lines at the water pump, first in side to water tank then out to faucets. I don't have the four way valve but it should be able to be set to different positions for the same effect.
I have always blow out lines. We live in the arid Southwest where many have underground sprinkler systems that need to be blown out every fall when the irrigation ditches are shut off for the winter. It works.
I also remember the pre-pink stuff days when blowing out the lines was the only option (or maybe my Dad was just too thrifty to buy the stuff!)
As I understand it, the water heater and the water tank emptied can freeze the little residual with no damage because there is room for expansion of the ice. The grey and black tanks would be fine but not the drain plumbing upstream of the dump valves.
I would not try the hose end fertilizer sprayer as it would dilute the the pink too much.