Back when I did my own winterizing, I blew my heater out, but then pumped -100 propylene glycol through it. Easy to do. I accessed it with an $8 RV pump at the connector on one of the heater hoses in the bilge. These days, I pay my dealer to do it. He pumps -100 propylene glycol through the whole engine, including the heater. Works great...it sits in there all winter, and in spring I just launch it, fire it up and we're good to go. I went 6 seasons on my last impeller.
'04 MariStar 230VRS/MCX