Three ways to winterize..
Wet method, Pump pink stuff in the lines then have fun getting it all out come spring.
Dry method, Pump air in the lines,, No problem with after taste. If Air ever freezes.. De-winterizing not going to be a problem,, or happen. (We will all be deceased and froze solid).
SOUTH method.. I see you know about that one.
I recommend you open all valves, low point and faucet, Drain the water heater and bypass it, then make like Gabriel with you air compressor and BLOW BLOW BLOW, use a regulator set to like 50 PSI, and blow till you either run out of air or stop getting water out the low point drains.
Wait for compressor to recharge and do it again
Five to 10 times or till you no longer get any "Spitting"
Pink toilets and drains only.
job done.