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.

Speak Your Mind