The boat sinking was just to get your guys' attention ; ) Water won't come through the hole when the engine is off.

I like the advice about putting the original caps back in though so I just don't have to worry about it. However, the reason the expansion plug was in in the first place was because the previous owner said he was having trouble getting all of the water to come out. When I winterized it last fall I pulled that plug out and extra water did come out. Maybe this is because the previous owner and I live in the same neighborhood and our driveways sit at similar angles? Maybe there's something weird going on with how we're parking the boat and how it allows water to drain?