Nice video, new owner here. Seems like the oil/ filter change should be done first to start the engine with water flowing. Then drain all water plugs and lines?
Get your self a air line fitting and some 3/8 hose the fitting fits on the oil drain line and the hose fits on the end than your plastic line fits in the 3/8 hose. No more pushing the plastic line into the drain hose. Much cleaner. Also does yours not have a water flush fitting on the water strainer?
Wait a minute, so you removed a the plugs to winterize , and drain, but the started the engine to verify correct oil level. Did you fire it dry, with no water through the bottom intake?