I have 6.2l Seacore engines. Is winterizing add simple as using the blue pump to drain most of the water, seal off out drive water pickups, and then fill sea water system at the port for fresh water flush....it is right by the heat exchanger. Fill it up, then start it up for a few minutes, and let coolant be pushed through engine. This should get antifreeze through engine raw water side....I think
It would be easier than testing to suck coolant up outdrive.