Used a 1 inch drill bit and drilled 2 and 1/2 to right of center anI found this cool plug at Boaters World for $9.99. It is kinda of hard to see but there is a 1 way floater ball that will prevent "most" water from coming back in if you happen to forget to screw back in the transom drain plug before launching.

The other cool feature is that the plug has a hole in it so you can loosen and tighten it with a wrench, screwdriver or a nail OR even chain it to the hull so you never lose it or have to hunt for it.

I plan to install it soon.

I am also seriously considering installing these in my 4 thru-hull fish boxes and 2 rear seat storage boxes.d 1 and 1/2 inch up.