My sump is about 30 feet from the tank with very minimal drop ran 2 inch drains and 1.5 inch returns. All the corners were done in double 45s to try and have a gradual corners as well.
Here shows a 1 inch drain would only carry 600 GPh
http://www.reefcentral.com/calc/drain.php
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360 gallon sps reef, 180 gal sump, bubble king supermarine 300, 4xmp40Wes, 2 x 6215 tunze waveboxes, 4 ghl mitras
360 Reef Tank