Drain pipe size question

[saltwater2999]

Right now I'm just trying to figure out what size pipe I should use for my system if I'm planning on have two 700 gph return pumps. My goal is to create a overflow with a full syphon to make it the quietest. I was thinking at full syphon a 1.5" pipe would work. Any comments

[thegrun]

Here are your flow rates for PVC drain pipes. To make a drain quiet you need a second emergency drain line sized to handle the water full flow (1400 GPH so a 2" single emergency drain or two 1-1/4" emergency drains lines in addition to the primary drains) so you can use a gate valve on the primary drain line to restrict the flow so the water backs up to near the top of the drain line. If you don't back up the water you get a loud waterfall noise.
½” 175 GPH
¾” 350 GPH
1” 600 GPH
1.25” 950 GPH
1.5” 1300 GPH
2” 2200 GPH
2.5” 3200 GPH

[saltwater2999]

So you recommend going with a 2" PVC pipe and just put a gate valve to adjust the flow. And yes I do plan on having the emergency pipe already