I moved my pics around, and so the links went bad. Unfortunately, I can't edit the original post anymore, so here's a new post with the pics in place.
First, here is BeanAnimal's original description of the system:
http://reefcentral.com/forums/showpost.php?p=11752972&postcount=1
Here is a link to the overflow:
http://synergyreef.com/product/16-synergy-reef-overflow/
This is the piping configuration I used inside the box:
From left to right: open channel, emergency standpipe, siphon.
The open channel has a 1/4" hole drilled right into the top of the elbow. I eliminated the air line, because I wanted to be able to close the lid on the Synergy Reef external box. With the lid closed, there is no sound from water flowing at all, either from the OC or through the bulkheads. The water level bisects the horizontal section of the open channel, so it is below the air hole and the emergency standpipe, but completely submerges the siphon. Here is a view from the top, with the system running so you can see the water level:
You can tell from this view that the siphon is completely submerged, and the open channel is not. This is important, keeping the air hole above water level under normal conditions. Not only that, but the water level also bisects the bulkhead openings, so that it flows directly through without an elevation change. No sounds of splashing, flowing, or trickling from the overflow.
External plumbing from the box:
And finally, where the drains exit into the sump:
In this picture, the system is running at full 600 gph. And you can see there are NO bubbles coming from any drain, making the system completely silent, as designed!
The two outer drains are the siphon and open channel. They terminate about an inch below the water line. The emergency center drain terminates above the water line, because it stays dry except in an emergency situation, and in that case I want no obstruction to flow.
On startup, the system purges air from the siphon within 10 seconds. I attribute this to the siphon line being lower than the OC, and so it fills more quickly and can start its purge before the OC starts to take some of the load of draining.
All the drains are 1", but a single 1" drain running at full siphon can easily accommodate the 600 gph of flow I'm putting through it.
I've tested the system against all failure modes, and it holds up. When I close off the full siphon, the water level rises until it covers the air hole in the OC. It immediately converts to full siphon and water level drops to the level of the air hole. Air then starts getting sucked in, making noise, and the water level holds steady there.
Closing off the OC completely would cause water level to rise to the emergency standpipe, which would then become the new OC.
The system can be shut off completely, and when restarted air purges out of the siphon within 30 seconds. Everything works as BeanAnimal describes.
Shouldn't really matter as it it just the secondary drain and shouldn't be used often, if at all.
