The Definitive Guide to Grease Traps

The Definitive Guide to Grease Traps

You may have never even heard of a grease trap, however they are a common feature for retail businesses that have anything to do with food preparation, including restaurants, cafes and commercial kitchens.  Essentially their job is to prevent grease and other organic waste from getting mixed into the main sewer of the Water Corporation (the water services company responsible for providing water, wastewater and drainage services in Western Australia).  Anything other than sewerage that gets into their main line will work its way into the city’s pumping stations, causing a build-up and damaging their critical systems.  This can lead to costly and time consuming maintenance for the Water Corporation, as well as poses the risk of the material spilling over and polluting waterways in the local vicinity.

As a result, and in line with the Water Services Act 2012, all businesses that are involved in food making must hold a permit and have an appropriate grease trap and drainage pipes.  Owners of the premises must also ensure that the traps are regularly maintained and pumped out to keep them functioning correctly and safely.  Let’s look at some of the factors that you should know if you’re looking at installing a grease trap, or having an existing trap one pumped and cleaned.

How do Grease Traps Work?

The beauty of grease traps is in their simplicity, with their basic design almost unchanged in over a century.  At its heart is a very simple concept, that fat, oil and grease (also known as ‘FOG’) is lighter than water, and will float.  The trap itself is a well, with an inlet and outlet to the tank, with baffles positioned at different levels to catch the grease as it enters from a sink drainage pipe.  The FOG will remain floating, and any other larger or heavier food debris will sink to the bottom of the trap, with a flow control help preventing the water from washing it away into the sewerage system.  This natural separation in the FOG and water makes it unnecessary to have filters or anything else that separates the materials.

There are guidelines to how the grease traps should be installed, including what needs to connect to it from within your kitchen.  All waste water from areas where food is prepared must flow into the trap, such as dishwashers, floor wastes and sinks.  Traps should also be installed as close as possible to the source of the FOG, with shorter pipes less likely to get clogged with the material than longer ones.

On the outlet side of the grease trap, there is an industrial waste sampling point (a ‘IWSP’), which is where the Water Corporation can visit the premises and test what is coming out of the trap.  To ensure it is fully functioning, a grease trap must be cleaned out or pumped on a regular basis by waste experts who can take the material away for safe disposal.


All grease traps serve the same purpose and are similar in design, however they can vary in size and the type of materials they are made out of.

The majority of grease traps for food preparation businesses are made out of lightweight and strong HDPE plastic.  This makes them easy to install and to maintain on a regular basis.  Grease traps made out of concrete are less common, however may be specified during installation projects which involve a hydraulic consultant.

There are pre-treatment size requirements for retail food processes, with 1000 litres being the minimum size trap, ranging right up to 5000 litres as a requirement for a hotel or function centre.  For the majority of small to medium sized restaurants (with a capacity of from 1 to 69 seats), take-aways, cafes and food court shops, a 1000 litre trap will be sufficient.


While it is difficult to estimate the cost of a grease trap for your business, a rough guide of an average price for installation would range from $5,000 to $20,000.  There are many factors that will determine the final cost of the project, including the size of the trap to be installed, as well as its positioning, the amount of excavation that may be required and the drainage systems that might be needed to accompany the grease trap.  Grease traps can vary in cost depending on the material they’re constructed from, with plastic and concrete being the most common.

In some cases with complex installation projects, sewer systems may need to be diverted or new ones may need to be built to accommodate the grease trap system.  This can obviously increase the overall price of the job with labour, materials and installation costs.


According to the Water Corporation, as an owner of a business with a grease trap, it is your responsibility to keep it clean and have it pumped out on a regular basis.  All traps need cleaning after a period of time, with the frequency generally determined by the size of the trap you have, and the nature and volume of the FOG your business may be producing.

Having your grease trap pumped out can occur at the same time as cleaning, or at a different point, however the frequency with which you need to have it completed is mandated by the trade waste permit you receive when the trap is first installed.   Under the permit you must:

  • Ensure your grease trap is pumped out within the specified timeframes
  • Report the pump outs to the Water Corporation within 7 days of it occurring
  • Use a licensed liquid waste contractor
  • Maintain responsible and healthy habits relating to FOG in your business

You may apply to have the frequency for pump outs altered or re-assessed by the Water Corporation, however a charge for the assessment will be applicable, and it will involve a number of inspections of the trap to determine the amount of use of the system.  Keep in mind that a re-assessment may also result in you having to pump out the trap more frequently.

The Water Corporation monitors their systems carefully, and any noticeable build-up of FOG in their pumping stations or the sewerage lines can mean they will need to investigate the source of the problem.  In some cases this may mean they use CCTV cameras to trace the FOG back to the offending business, with resulting punishment if they are found to be not maintaining their grease trap correctly.

In some cases a grease trap will need to be replaced, especially if it is old, leaking or is developing issues caused by general wear and tear.  Although repairs can be conducted, it is sometimes simply better to have a brand new system installed.


Superior Plumbing are the experts in installing, unblocking and troubleshooting issues with grease traps for all types of retail and commercial businesses.  We can provide advice and assistance with all aspects of replacing your old grease trap with a brand new one, from the most suitable trap for your requirements, as well as any additional plumbing work that may be required for the new system such as relocating pipework.