I've not seen black egg crate, the bad thing about that would be difficulty getting your U tube through. I think with the openings you've got now that would be perfect.
I'll get around to taking some pics of my tidepool overflow it's reasonably adjustable and it can flow about 600gph. I've modified an older overflow to flow a bit extra but I'm still not "pleased" with it. I'm using 1 1/4" PVC and it still wont flow 300 gph.
Doug
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