I was asking if mark's setup was possible or if anyone had it setup like that.

One hole per overflow with 2 corner overflows.

Thanks Mark!

Only issue I could see with running primary in one and emergency drain in the other overflow is water becoming stagnant in emergency's chamber.

Was going to raise the lip height of the overflow with emergency but never did. What I ended up doing was drill a hole in the side of the emergency drain standpipe so I have a small but continuous movement of water. My sump can easily handle the full volume of the chamber in a power outage but I still drilled it up near the top of the standpipe and have a 1/4"OD tubing running to the bottom. Since hole is near top, that's my siphon break.

I'm also running a 20g fuge separate from my sump and just tee's the primary drain. About 200gph to the fuge rest to the sump. Here's my post on converting from dual Dursos to the Herbie.

I was planning on raising the emergency overflow lip.

Is there a benefit to letting a small amount of water flow through emergency overflow?

think it's a either or type thing. Raise the lip or if both OFs same height, move the water a bit. For the emergency drain line itself, can't see advantage of running water through it, though see some conventional Herbies always running a little moist.

btw since you only have a single hole in each, seems a Bean is out.

Why not use all drilled holes for drains so you can setup a dual herbie, then just run your return behind and over your tank.

And the dart isn't a bad size for the tank, a little big but nothing it couldn't handle. Personally I would go with a good quality internal pump for noise and reliability but that's just my personal preference.

The way he described his overflows (post #8), the extra, or return holes are drilled outside of them. He'd have modify or move the overflows to include these outside holes (or plug them?) to do the Herbie using all drilled holes.

IC, in this case I would personally wouldn't use a standard herbie design, I think using a second overflow with the purpose of emergency only will lead to problems as already stated such as stagnant water even if it's higher as water will still sit around the bulkhead which could lead to mold growth and that algae smell. What I would do is use the one overflow as a primary to take the majority of the flow, you can still set it up with a gate valve but adjust it so a small amount of flow still goes through the second overflow which would have a durso standpipe. Setup the durso so it has a small siphon break hole and a longer downspout, if the primary clogs up the durso will siphon under the higher load to prevent tank overflow. The second overflow will need to be slightly higher but nothing significant, a layer of silicone should be sufficient.

sphelps is right with the problem waiting to happen. I'm currently runnign that setup, since i only have 2 holes drilled in my tank and i'm running a herbie. A herbie emergency drain should be bigger than the original, mine is not. I've got the main fairly restricted, but if it was to 100% plug, there would be problems, i don't think the second overflow could handle 100% flow. It would top the overflow and still make the drain, but my tank would be near/at 100% full.

As for the stagnant second overflow, i have a 1/4" hold drilled about halfway down my emergency drain, keeps a bit of flow, but still lots of sediment at the bottom of the overflow.

But yes, i would recommend another hole drilled to run a herbie (a 2" if your main return is 1.5"), it's silent. There's lots of other setups around too, i like the stockman, or the Beananimal mentioned is a great one as well. All preference.

From first hand experience have to disagree that a modified Herbie is a problem waiting to happen. Mine's been up since last October, water in the 2nd chamber can't be that bad as snails don't seem to find it a problem. As for sediment, what's in the overflow is what's left from when I pulled out the Durso. If it was a problem guess I could just siphon out when I did a water change.

Idea for the emergency being a Durso is interesting but since I'll need to worry about flooding at 2000gph if the primary became blocked, I'd be reluctant having the emergency standpipe anything other than a open pipe.

Drain size, here's a calculator for a guide, (towards bottom). 1.5" should be able to handle a Dart.

Maybe I'll start with a durso or stockman setup first and if that's not quiet enough, try something else?

Beananimal is out, I have single-hole corner chambers.

Thanks for the input!

-Rob.