So I ended up with 2 fish in the overflow box. I tried to drain it, tried to catch them, etc, but it is really hard trying to go across the tank to see what is down the overflow when the tank is up against the wall. I finally called my LFS and they walked me through the process. It ended up being so easy and took about 10 mins in total. This was with a Planet Aquarium with the overflow box in the back, but am happy to copy the directions below...
From my LFS: Directions for getting the fish out of the overflow
So, in your overflow, you have your drains, and your returns. You should be able to do the following:
1 - Cut off your return pump
2 - Take your filter socks out of your sump temporarily
3 - Pull one of your drain stand pipes out of your overflow. (In the middle back of your tank, is your overflow box, the larger pipes in the middle with the bigger black dome thing on top are you drains. Pull those out and prop them up so the water drains out of your overflow box. The fish will then go down through your bulk head and into your sump, or they should)
4 - Collect your fish from your sump and put them back in your display. Catching them is not always easy, but should not be too bad in that sump.
5 - Put your stand pipes back in.
6 - Put your filter socks back in unless the fish are still down there. You can leave them out if need be it won't hurt a thing.
7 - Turn your pump back on.
The fish did not go into the sump - that would have made it too easy. There was about 1/4" of water left in the overflow and both fish were at the bottom. I quickly caught each one and put them back in the display tank.
They are both doing great and seem to be quite happy back with the rest of the fish. Hope this helps!! Good luck!
