Herbie method for Dual Overflows

Many aquariums with dual overflows can be retrofitted to use a siphon-based Herbie Overflow. This post assumes a bit of understanding of the system so read through that if you’re just starting out. Having more than 2 pipes available allows for a secondary dry emergency line in some configurations. Those may be considered a Bean Overflow by some people.

It has been a common practice in the past for builders of these larger reef tanks to set them up with the “reef ready” design. Inside each overflow are two holes for bulkheads; one for the return, and the other for a single-pipe-drain. Some common brands are Marineland, Perfecto and a few others.

Some universal rules:

  • If you have two pipes in the same overflow with different diameters, then always use the larger one as the emergency drain. You want it to have maximum capacity that matches or exceeds the capacity of the siphon drain.
  • Don’t “Tee” any of the pipes with the Herbie for best results
  • With a long tank that has 2 overflows, it becomes more important to make sure it sits on a level surface so that the overflows take on the same amount of water at each end.

Reasons to Update from a Single Drain System

Single-pipe-drains require no adjustment, but have several drawbacks. Air and water move through the drain at the same time, creating noise. There are many contraptions that attempt to quiet the drain with varying success (Durso, Stockman, Hofer etc.). If air moves down the pipe, there will be splashing down in the sump which can generate microbubbles or lead to salt creep. These drains also have only a fraction of the capacity of a siphon-based drain.

By converting the tank to use a siphon-based method like the Herbie or Bean method, the drains become silent and get more capacity to move a lot of water.

A note about “Reef-Ready” tanks

Reef-ready tanks may have small bulkhead openings compared to the size of the tank. Do your homework with flow rates and required turnover if you have a tank with anything less than 1″ bulkheads in the overflows.

These tanks often come with a return line running up through the overflow box. These are often changed into siphon standpipes with a Herbie conversion because they are often the smaller of the two in diameter.

Option 1: Independent Siphon/Emergency in each overflow

Due to the sheer volume of a tank that has two overflows – It’s often a really good idea to have a 2nd emergency line available.

With this setup, both overflows have both a siphon drain and emergency drain — like you would on a tank with only one overflow.

You may want to adjust one siphon so that it takes on less water, just enough to provide adequate surface skimming. The other siphon can then be used as the main point of adjustment, and can be the one that is easier for you to access.

With the amount of water that an single Herbie can move, having two means the siphon valves will be closed-off a considerable amount. This can mean finer adjustments are necessary.

Having two independent overflows can result in having to do too many fine adjustments which can be tedious. For this reason, some people choose to go a different route.

Option 2: Joining the two overflows so they act as one

If the two overflows can be connected with a “Tunnel” of sorts, then they will act as one overflow with two weirs. This is commonly known as a Balance Pipe. A pipe that spans behind the tank, passing through a bulkhead at the rear of each overflow. It could also be done inside the tank, but wouldn’t look very good unless covered with sand.

You will want the bulkheads for a Balance Pipe lower in the overflow so they are always submerged (below the siphon intake). Larger diameter pipe will allow water to equalize between the two overflows quickly. Strainers on each bulkhead opening will ensure that nothing gets in the pipe.

This setup allows for 2 pipes to be used as a typical siphon / emergency combo. The third pipe is used as the primary emergency and the fourth pipe can be used either as a secondary dry emergency, or as a return output running over the overflow wall into the tank.

Option 3: Only using one overflow and disabling the other one

If the diameter of the drains are of sufficient diameter — only one overflow may be enough.

Your main overflow would operate as a conventional Herbie drain setup with 2 standpipes (siphon and emergency).

In the unused overflow, one pipe is used as a dry secondary emergency, and the other as a return.

This method would makes the 2nd overflow dry. In order to keep it dry, you would have to slightly raise the level of the weir slightly. On this dry overflow water would only enter in the unlikely event that both the main siphon and emergency were completely blocked. If you don’t raise the weir on an unused overflow — it fills with water, and a chamber of nearly stagnant tank water is undesirable.

Option 4: What to Avoid – Teeing both siphon drains together

Some people wish to have only one drain line going to their sump, so they attempt to join the two Herbie siphons together. This is usually done below the tank under the bulkheads by using a “T” fitting.

This setup should be avoided.

You see, it is nearly impossible to keep the water level in two separate overflows balanced if they’re connected by the drain line. A siphon will always function as one unit, so the two intakes will affect each other no matter what. No configuration of valves or having equal lengths of pipe will change this.

The reason is that there are slight variations in flow from each siphon, like algae on the strainer or overflow teeth. These variations will always be present and changing the flow in the pipes over hours or days. One line will always affect the other if they connect in any way.

Gaining control over the water level in each overflow is only possible with individual siphons, or by connecting the two overflows with a Balance Pipe. A siphon must have it’s own independent valve and pipe extending down into the sump water to a chamber with a constant water level.

What about Teeing both Emergency drains together?

Never do that – Anything that lowers capacity of an emergency drain should be avoided at all costs.  Ideally an emergency drain will go full-siphon, and this would be hindered by being Tee’d into another pipe. Siphons also can’t start as easily with with horizontal runs in the drain line.


  1. Kenrick Venett says:

    What are your thoughts for joining the two siphons underneath the tank instead of a balance pipe between the overflows (inside or behind the tank). The underneath will be balance pipe with 45 elbows to minimize horizontal runs. Admittedly there will be a slight horizontal run when the two siphons come together at the tee but minimal. They should be pretty close to being balanced. If they are balanced then You can balance the pump with a single valve.

    • The siphon must be a totally separate pipe. A balance pipe that joins the two overflows must be completely independent. Without one, it is impossible to have the water level in both overflows the same. The problem is that the two overflows never draw in the same amount of water. Small variances between the two in overflow volume, weirs, or plumbing can cause this. One side draws in more water at any given time.

      These little variances mean the water levels inside both overflows are different. “Pretty much balanced” isn’t going to help you, even if you lucked out and it worked like that (for a while). You can only adjust a siphon against an overflow that functions as one unit. Two overflows can function as one unit when you have a balance pipe – but unfortunately that’s the only time you can use a single valve and a T on your two siphon inlets.

      Thanks for commenting – going to add some illustrations to this page to make it more clear.

      • Hello! Do you have any images, or a video example of the whole balance pipe practice? I’m having difficulty visualizing the way you explained it. Is it similar to the coast to coast weir pipe that mrrvbrown uses?


        • I will be adding 3D renders of each setup to the post very soon, so it will be easier to understand. The balance pipe is simply a pipe that joins both overflow boxes. Think of 2 buckets. If you were to drill the bottom of each, then connect them with a pipe, they would be a single vessel. If you were to fill one with water, the other would always have the same water level. I hope this helps.

  2. Julius Taylor says:

    I’m converting my 150 gallon with dual Durso overflows to a Herbie setup. Rather than try to balance two drains or have a dry side, I’m running one of the old return lines back into its overflow. The water flows up through the weir. The other side has the main drain and emergency (converted from its return). I’ve removed the drain pipe from what is now the return box and just have its bulkhead closed off. I’m not sure if I will use a second emergency or just install a water level detector to stop the return pump.

    • I haven’t heard of that before but can’t see a reason why it wouldn’t work. I would probably not do it though because you can’t take advantage of the return line outlet as a source of flow in the tank.

  3. orebro flughaven says:

    Hello gmacreef,
    Thanks very much for your insightful articles. I’ve learned quite a bit. I’ll be taking delivery of a custom aquarium. This is to be used as a freshwater CO2 injected planted tank, and for years, I’ve only ever used closed loop systems so I’m completely unfamiliar with sumps. The tank is 180G and in the sump will be two independent identical DC return pumps each rated at 2000 GPH. My target turnover rate will be 10X so I assume each pump can be set at 50% to 70%. All holes and tubing are 1.5 inch dia. I don’t think that in reality the total return rate from the pumps will approach 1800 GPH but lets assume for the moment that it will

    I’m intending to use option 1 in your article above, i.e. two external boxes each fitted with 1 siphon and 1 e-drain with all four lines independent.
    I understand all the points you listed above as well as in your introductory Herbie article, but I haven’t seen any instructions as to how to get started configuring and testing, particularly for this configuration. I’m quite happy to have both siphons running some portion of the total return and to have both e-drains having some amount of trickle. I’m not interested in symmetry as I reckon that would be difficult to achieve. I’m also not in the camp that insists that an e-drain be dry, however it seems there may be some benefit in configuring the system so that it functionally approximate a Bean system. Again, however, it’s not really clear how to proceed.

    Do I set both pumps to 100% with both valves full open and then begin closing one of the valves until that box’s e-drain starts to trickle?
    Is it better to start with the intended pump setting first? Should I start with only one pump running?

    Perhaps this is all old hat to reefers but it seems unclear to me exactly what the best procedure is for zooming in on valve configuration.
    I could see myself turning valves and adjusting pump speeds endlessly without getting anywhere.

    Any advice you could offer would be greatly appreciated.


    • Thanks for your well written and clear comment. The “10X rule” is one of those fish tank adages that that people like to repeat because it’s a nice round number. If the rule is followed, it will result in a loud, inefficient system in many cases. Return outlets also can’t provide the same kind of random flow that newer powerheads can create in the tank. Some of it has to do with personal preference, but if you read through Creating Flow in the Reef Tank you might start to agree.

      For comparison, my 150 gal setup with a 40 gal sump currently uses a Danner Mag 7 pump. It pushes around 500gph with my 6′ foot of head height. A bit more flow would be nice, but then it would start to make more noise which I don’t want.

      The main suggestion for you would be to only use one of the pumps.

      Unfortunately there aren’t any tricks on how to start adjusting 2 siphon valves. Start with the valves fully open then start inching them closed alternating each one. If the valves are far apart you might get someone to help to man the other valve.

  4. I have a 120G with dual corner overflows. Each overflow has a 1″ and 3/4″ bulkhead. Would it be possible to combine the plumbing for the siphon and emergency standpipes for each overflow, such that only one bulkhead is consumed. The herbie method seems superior to my current Durso, but I don’t want to lose any return bulkheads.

    • The siphon and emergency lines always need to be separate and discreet to work properly. There is no way around it unfortunately. This is why people convert their returns into drains so often.

  5. I have a question for a possible hybrid herbie if possible.
    I have a 150gallon reef ready aquarium. Has 2 corner weirs both durso and return lines come up this.
    The durso drains are 1 and 1/4 inch reduced to 1inch that sets into the bulk head. The return lines are 3/4.

    Could I keep both return lines as returns that are in the weirs.
    Convert the left weir durso drain into a herbie full siphon and convert the right weir as the emergency?
    What would be the pros and cons of this method?
    Flow from the sump to the display would be very minimal but the tank will have more then enough flow from (2) gyres that will be in the tank.

    • You could only do it as you described it if you did the balance pipe method. That way, the 2 overflows would function as one vessel. The Pro – you could keep the return lines as is. The Con – might be a lot of work to drill new holes for a balance pipe with bulkheads.

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