What Sized Drain Pipe For 500-600 GPH?

Id go do a single 1.5" or drill a pair of 1" holes. There's no real need to run a drain so close to capacity. If you're gonna take the time to drill a tank just drill it large enough to suit your needs. Any screw up or blockage is gonna put that 1" over the edge.

I think alot of people will disagree with me but 600gph is really pushing it for a 1" pipe. Unless you're running a full siphon, 400 gph is more realistic

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I'll be using a 2-3/8ths bit for a 1.5" bulkhead per glass-holes and a few other sites.

2-3/8" is right for a 1.5". You need a 1-3/4" hole for a 1" bulkhead, it's really not that much bigger.

http://www.wetwebmedia.com/BulkheadFloRateArt.htm

This is a really good article. ^

Basically a 1" will flow 360 gph or so before it becomes a partial siphon. That's when the drain makes alot of noise gurgling and flushing. It's switching back and forth between an open channel drain to a full siphon, there's not enough flow to maintain the siphon and it breaks, then there's too much flow to maintain the open channel drain, and it fills back up again and the siphon restarts. You see what I'm getting at.. one day something may partially block the drain and the partial siphon may not restart and you've got water on the floor. On a multitank system the consequences are higher.

I have no problems running 1" drains well over capacity, but if its the only drain on the tank then you are just asking for trouble. It's very True you can push well over 600gph Through a 1" drain. I've ran 1700gph through a 1" full siphon and a 3/4" open channel drain (durso) on a beananimal setup with a second 1" dry stand pipe acting as an emergency drain

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Heres a pic for fun

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