Many will tell you that it's silly not to do anti-freeze. IF you do, you need to be sure that either the thermostat is pulled or the engine is up to temp to ensure it's getting into the areas behind the thermostat. OR they say that you DRAIN first completely, then fill with anti-freeze. This seems the best suggestion.

Personally I subscribe to the "drain completely, there's nothing left to freeze" camp. The downside to this is that the Pro-antifreeze camp will say that the antifreeze makes it so your empty block isn't getting corrosion.

If I was going to use antifreeze, I'd add a flush pro valve or intert a brass ball valve Tee so you can tap the garden hose into the intake line. No way I'm going to mess with a plunger whatever setup. Sure the flush pro is expensive (my boat already had one) but it's dirt cheap to add a brass ball valve tee so you simply connect the hose and turn the lever.