Overflow Relief Gully

An Overflow Relief Gully (ORG) is a fitting located outside your home that releases sewage in the case of a sewer blockage. If a sewer blockage occurs, the ORG fitting should pop off to release the excess pressure and direct sewage so it does not enter your home. ORGs should only be altered by a licensed plumber/drainer.

How does it work?
If installed correctly, an ORG works because it is fitted at a depth that is lower than any other sewage outlet in the home, particularly the shower base and/or toilet (where an internal sewer spill is most likely to occur).

In the event of a sewer blockage that causes the flow to backup, the ORG is designed with a loose fitting grate that should be free to “pop off” completely. This allows the sewerage flow that has backed up in the pipes to escape at the ORG, outside, rather than inside your home or business. As it is located outside, the interior of your home is more likely to be protected from a sewer spill.

When an ORG is not functioning correctly the property damage and health risks associated with sewage spilling inside or under a property are greatly increased. 

If the ORG is raised too high it may be above the level of the floor wastes in the house and in the event of a blockage, sewage in the sanitary drains may back up and overflow out of the floor wastes inside the house. If the ORG cannot be raised an inflow prevention device may need to be fitted to the ORG.

You should never cover your ORG as this may prevent it from working in an emergency.

Plumbing regulations require ORG’s to be installed a minimum of 150mm below the lowest fixture, which is usually a floor waste or shower, to prevent internal sewage surcharges and 75mm above the surrounding ground to prevent rainwater inflow into the sewer system during rain events. Rainwater inflow to the sewerage system can cause overflows which can result in public health and enviromental risks.

Make sure your ORG is not:

  • underneath the property as a result of not being moved when a house extension was built
  • covered by landscaping or garden beds
  • covered or obstructed by an objects such as pot plants or pipe work
  • unable to pop off because it is corroded, filled with silt or concreted in
  • The grate is not prevented from popping open due to being corroded, filled with silt or permanently fixed in concrete
  • Connected to stormwater downpipes.

Make sure your ORG has:

  • a clear drainage path (so spills drain away quickly without causing damage and not build up around the ORG itself)
  • a fitting that can pop off completely
  • been installed at the correct level (100mm above ground level when situated on grass surfaces or 50mm above paved surfaces).

What does it look like?
The shape and size can vary greatly. Generally they are between 100mm and 150mm in diameter. Some are made of plastic or metal alloy and some have a pre-cast concrete surround. As ORGs have been installed since the late 1970s, many different models exist. We strongly recommend you install an approved model that is unhindered and pops off completely in an emergency.

In some properties there are fittings that may look like an ORG that are called ‘disconnector gullies or gully traps’. These can easily be converted to an ORG, provided it is lower than any other waste outlets in the home.

Do all homes have an ORG?
Most properties constructed after 1976 have an ORG, surrounded in concrete, near an external wall (or in special cases they may have a reflux valve). Buildings connected to the sewer prior to this date do not have an ORG unless additional work has been carried out since 1976. We strongly recommend that all homes have an ORG installed. When it is not possible to install a complying ORG, a reflux valve may be installed.

Locating your ORG
Relief gullies are usually at the end of the house sewer system, close to the house. From the gully the sewer line heads straight for the sewer main connection. The relief gully is always set lower than the floors in your house that have floor wastes, such as the bathroom, toilet and laundry.

Are ORG’s covered by regulations?
There are plumbing regulations that apply to the installation of ORG’s (National Plumbing Code AS 3500 1998). If you already have one installed, a licensed plumber should make an assessment as it may need to be repaired or replaced. If you don’t have one, contact a licensed plumber for a quote.

ORG responsibility
It is the property owner's responsibility to make sure their home is fitted with a properly designed and operational ORG.


A licensed plumber should be contacted if you do not have an ORG or require an alteration to an older fitting. All costs are the responsibility of the property owner.


Download: How to help prevent sewage overflows on your property Fact Sheet (PDF)

                  Looking after your water supply and sewerage infrastructure Fact Sheet (PDF)


    Did You Know
  • A running tap, in an average hand basin, uses up to 20 litres of water per minute.