A strainer on the main drain would solve that problem

Soooo just out of curiosity, who sells those Durso kits?

Rich did at one time on RC. He has his own webpage or had. Cant say or not if he still does. Easy to build. I have built dozens and never a problem.

gack! Have you done this yourself? This is exactly how I had my tank set up and it was a constant never ending nightmare. I finally converted back to a durso with all the micro bubbles, noise, and salt creep that I hate because I couldn't deal with the herbies anymore. The levels in my overflow boxes would randomly drift over the course of the day, sometimes with one emptying half way creating a splashing water fall, while the other would fill completely. This was true whether I set the levels with a single gate valve downstream of where they connected, or two gate valves upstream of where they connected. It was the most unstable overflow system I've ever seen. Further to that, I'm not sure if this is a Herbie issue or them being plumbed together, but they were INCREDIBLY sensitive to water level changes in the return chamber of the sump. If I had it throttled just the teeny tiniest bit too much, the return chamber level would fall, and my ATO would kick in (it's a powerful pump that moves a ton of water as it comes from the basement). Then the level would reset below the ATO sensor, causing the ATO to fill the return chamber again. This happened very slowly over the course of 3 days once until suddenly water started pouring down my emergency drain and the SG of my tank had fallen to 1.022

I'd never in a million years run a Herbie with dual overflows plumbed in to a single outlet again. Maybe it's just me and I'm a dolt and set it up wrong and you've had a different experience, but that was easily the biggest error I feel I made with this tank.

Not herby or durso , but an interesting read

http://www.beananimal.com/articles/h...-aquarist.aspx

http://www.beananimal.com/projects/s...ow-system.aspx

I did the bean animal. Pretty easy. Did it on my Ada 60p tank.

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Yeap had a customers tank setup this way back in the day. You need riser tubes in the overflow boxes and back ups in each one as well. If there was a slight imbalance the water level could only drop to the top of the riser tube and would correct itself quickly after hitting that. I was only there briefly every month or so and never saw a problem, rarely had to touch the gate valve. They did mention a brief slurp sound from time to time but nothing constant so it all seemed fine to me. I assure you trying to maintain separate gate valves on each would prove much more challenging.
If you do find a constant imbalance it would be due to more pipe friction from one overflow. This can result from smaller pipe sizes with higher flow rates (high velocity) making one side more restrictive quite easily, especially if it has a longer run or more fittings before the gate valve. You could easily fix it with an additional valve on that line but still connecting both lines to a single valve. The extra valve would just allow to add more restriction to the less restrictive side helping the sides self balance easier.
It's not a perfect system by a long shot but a herbie on a dual overflow has challenges you have to be willing to accept. Still better than Dursos IMO.

Ok so I'm prepping the plumbing for my new tank.
The emergency drains for my Herby. How high should they be in relation to the teeth on my coast to coast overflow? Top of the high part of the teeth or half way up the teeth? Sorry for the stupid question but I've only ran with Dursos? Pics to compare would be great
My overflow is 29" deep. Was thinking on 16" height for main drains.

I think it's more of a personal preference thing, the higher you go the quieter it will be but lower will give better surface skimming IMO

I go half way down from the teeth but what I would suggest is to not glue the standpipe in and try a few different heights to see what works best. (I never glue my standpipes)