Danny, I built an outside overflow for my 60, I went with 1/4 inch glass, and did it 3 inches wide, next time I'd go at least 6 inches wide to make it easier to put my hand in. I simply cut the top of the tank with a 3/4 inch lip, the water flows over the top into the box and I have TWO down tubes going into my sump. It works nicely doesn't take away from the tank capacity and allows shrimp larvae to stay away from preditors. This does not address your desire for closed loop though.
Doug
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