You're right. The two rinse/rain drains that are
outside of the hatch-seal are merged with the standpipe drain. Water that enters any of those drains pours out of the same hole on the side of the hull.
There's also a
third drain, this one
inside of the hatch-seal, that's also merged the same way. I'd forgotten about that one — doh! That indeed is an overflow drain, just as you &
@keldrickw described it. My mistake!
My standpipe had four holes drilled into the cap from the factory, and those are the four holes I enlarged, because the original holes, in conjunction with the one overflow drain, weren't flowing out enough water, so water would get past the hatch seals pour out onto the deck. I usually fill the baitwell with pinfish and/or grunt — and because I don't have a standalone aerator, I have to run the baitwell pump "whenever I think about it" to keep the water oxygenated and at a reasonable temperature.
When I catch fish and place them in the rear livewell, I have to run the pump full time, or the water in there heats up so quickly that the fish die.