Never leave the plugs out, unless those piece of crap plastic plugs. No plug in cast block or manifold and you will have to tap it out in the spring. They rust real bad.
When you work at a marina (as I do) and you cannot trust your customers not to try taking the boat out "one more time", you really don't have any choice. And yes, we've had folks take a boat out after we winterized it and try to blame a cracked block on us. I've never had to tap anything out in the spring, but we're 100% fresh water. In salt water, you might have a point.
