An overflow box is used to drain water from your display aquarium down into your sump or filtration system. The overflow box itself consists of a weir and drainpipes to get water out of your tank and down into your sump.

While there are several different types of overflows using a variety of different drain styles, they all accomplish the same thing - drain water from your display down into your sump or filter. 

An overflow box can be internal or external meaning the box is either inside the aquarium or outside the aquarium. Durso, Herbie, and Bean Animal refer to the drain plumbing itself inside the overflow box. These are the three most common water drain technologies you will see used on an aquarium. All of them can be used with either an internal or external overflow box.

Durso Overflow Box

Durso Standpipe

This is the most basic of the drains styles that only requires a single hole to be drilled into the tank. The Durso Standpipe was created by a hobbyist, Richard Durso, and was born out of the desire to quietly and efficiently drain water from the display aquarium down into the sump. In days past, noisy drains were problematic because the water would splash and gurgle as it passed through the pipes and down into the sump. The faster that water is moving, the louder it would get. The Durso Style drain reduces that noise level considerably when tuned correctly.

How it works

The Durso is easy to install and does not take up much space making it popular for smaller aquariums with sump systems and those DIY folks who like to build stuff with their own two hands. Instead of having the water crash down into the bottom of the overflow box, the Durso Standpipe allows for the water to rise and enter the drain through an attached elbow close to the surface as demonstrated in the diagram.

Technically speaking, the Durso Standpipe is the plumbing assembly above the bulkhead, inside the overflow box. Everything you need to build a Durso Standpipe can be purchased at a local hardware store using generic PVC pipe and plumbing parts. While the term Durso is unique to the aquarium hobby, it is an example of an "open-channel" style drain that does not engage a siphon.

Inside the overflow box, the drain pipe will typically measure 1" - 2" in diameter and will rise to about 2" below the weirs on your overflow box.  The larger pipe diameters can handle higher flow rates and can be reduced in diameter at the bulkhead before draining down into the sump. The end of the drain is then typically submerged below the water level in your sump to help avoid splashing noise and reduce salt spray. 

The standpipe has a small vent hole on the top elbow that prevents a siphon from forming in the drain pipe. This vent hole will need to be adjusted in diameter based on your flow rate. The lower the flow, the larger the necessary hole to prevent siphoning and water level fluctuations inside the overflow box.  

Tuning

To tune the Durso drain, you simply adjust the flow rate of your return pump. Make small flow adjustments until the drain runs quietly. You can use multiple Durso pipes to achieve higher flow rates should the need arise but in that case, you are much better off using a Herbie or Bean Animal Style drain instead.

Pros and Cons

The biggest limitations with a Durso Standpipe are the flow rate and the lack of an emergency drain. Although they take up very minimal space and only require a single hole in your tank, you do not have a fail-safe or backup drain should the pipe become clogged and there is a limit with how much water they can drain while remaining quiet.  

Herbie Style Drain

Herbie Overflow

When there is more at stake than just noise there are overflow options that also provide peace of mind. The Herbie Drain is an effective way to keep noise to a minimum while also helping prevent a drain disaster.

How It Works

The Herbie Drain is composed of two standpipes. One acts as the main drain pipe and creates a full siphon when pulling water from your tank. The other drain pipe is used as an emergency drain should the main drain become clogged and is just a bit taller (6") than the main siphon pipe.

This drain style is ideal for larger aquariums because you can move higher flow rates compared to a Durso drain. The main drain will have a strainer keeping aquarium inhabitants like snails, crabs, or foreign debris from getting clogged in the drain line. The strainer should be cleaned frequently to prevent a blockage and check the emergency drain often to ensure nothing has crawled inside the pipe.

The main drain is submerged roughly 2" underwater down in the sump to keep things quiet. The emergency or secondary drain can be cut about 6" above the water line so it makes noise and alerts the tank owner if the e-drain is engaged.  Under normal operation, the emergency drain should not get wet, and only when there is a problem will water flow through that drain.  

The main drain will have an adjustable valve to allow for fine-tuning of the drain siphon speed resulting in quieter operation and optimal flow through your aquarium.

Tuning

A Herbie overflow is adjusted using a gate valve on the main drain and adjusting your return flow rate. The key is finding the balance at which you're getting the flow rate you desired into the tank while still running quietly without surging, gurgling, or splashing.  

Start with the drain valve wide open, turn on your return pump and slowly dial back the valve until the siphon runs quietly.  Should you close off the drain more than 50%, you should slow down the return pump and start adjustments over again. The gate valve should only be used to make fine adjustments to the drain rate, your return pump is going to be the primary control over the flow rate. 

NOTE: It's best to use a gate valve on your drain pipe over a ball valve. The alternative Ball valves just don't give you the precision you need to adjust the siphon.  

Pros and Cons

The Herbie is a great system for a variety of tank sizes because it can handle higher flow rates without a drastic increase in noise. It will require two holes in your aquarium which means a Herbie drain takes up more real estate inside your tank. The ability to control the drain rate and the peace of mind you get with the emergency standpipe makes this a very popular option.

Bean-Animal Style Drain

Bean Animal Drain

The Bean Animal drain is a hybrid version of the Durso and Herbie style drains. It literately employs both drain styles to accomplish high flow rates while operating near-silent and provides the user with protection against clogs and overflow.

How It Works

The Bean Animal Drain uses three drain lines which means you need three holes in your tank or overflow box. The main siphon drain is a Herbie-style pipe, the secondary vented standpipe is a Durso drain, and the third is the emergency backup drain.

The reason this drain operates quietly, even with high flow rates, is because you can reduce the rate of flow using the valve on the main siphon drain to the point it operates silently. The Durso pipe then drains the additional water required to accommodate your desired rate of flow through the aquarium. With the Bean Animal, the two drains would be submerged below the sump water line for effective and silent operation.

The end of the emergency drain can be cut above the sump water level. Should it ever be in operation, the splashing into the sump will act as an alarm, alerting a hobbyist that something is wrong with the drain.

Tuning

In this case, your drains can handle a variety of flow rates so you won't have to worry too much about your return flow rate.  Simply adjust the main Herbie siphon to run quiet, and the Durso should handle the remainder. Should your pump be grossly oversized for the drains, only then will you need to adjust the return pump flow rate.

Pros and Cons

The Bean Animal is one of the best ways to move water out of your aquarium and into your sump. It is quiet, handles high flow rates, and includes an emergency backup drain. The downside is the amount of space required to get all three drains installed onto your tank and the necessary plumbing that goes with it.

Overflow Boxes
  1. Deluxe CS150 Overflow with Lid and Air Pump - CPR Aquatics
    CPR Aquatics
    Deluxe CS150 Overflow with Lid and Air Pump - CPR Aquatics
    $274.99

    Earn 8,220 Reward Points Earn 1,370 Reward Points

    $274.99
  2. Deluxe CS102 Overflow with Lid and Air Pump - CPR Aquatics
    CPR Aquatics
    Deluxe CS102 Overflow with Lid and Air Pump - CPR Aquatics
    $264.99

    Earn 7,920 Reward Points Earn 1,320 Reward Points

    $264.99
  3. Deluxe CS90 Overflow with Lid and Air Pump - CPR Aquatics
    CPR Aquatics
    Deluxe CS90 Overflow with Lid and Air Pump - CPR Aquatics
    $229.99

    Earn 6,870 Reward Points Earn 1,145 Reward Points

    $229.99
  4. Deluxe CS50 Overflow with Lid and Air Pump - CPR Aquatics
    CPR Aquatics
    Deluxe CS50 Overflow with Lid and Air Pump - CPR Aquatics
    $199.99

    Earn 5,970 Reward Points Earn 995 Reward Points

    $199.99
  5. Prodigy M Low Profile Overflow Box (700 GPH) - Eshopps
    Eshopps
    Prodigy M Low Profile Overflow Box (700 GPH) - Eshopps
    $169.98

    Earn 3,380 Reward Points Earn 169 Reward Points

    $169.98
  6. Prodigy L Low Profile Overflow Box (900 GPH) - Eshopps
    Eshopps
    Prodigy L Low Profile Overflow Box (900 GPH) - Eshopps
    $189.98

    Earn 3,780 Reward Points Earn 189 Reward Points

    $189.98
  7. LoPro External Overflow Box (2400 GPH) - Fiji Cube
    Fiji Cube
    LoPro External Overflow Box (2400 GPH) - Fiji Cube
    $274.99

    Earn 5,480 Reward Points Earn 274 Reward Points

    $274.99
  8. LoPro External Overflow Box (1600 GPH) - Fiji Cube
    Fiji Cube
    LoPro External Overflow Box (1600 GPH) - Fiji Cube
    $223.99

    Earn 4,460 Reward Points Earn 223 Reward Points

    $223.99