Grease Trap vs Grease Interceptor: What's the Difference and Which One Does Your Kitchen Have?

You are standing in the kitchen at close of service, mopping up, when the floor drain starts backing up. The plumber comes out, takes one look under the sink, and says your grease interceptor is full. You nod. But on your council compliance notice it says grease trap. Are they talking about the same thing?

Mostly yes, but not always, and the difference matters when a council inspector asks for your pump-out records.

What People Mean When They Say Grease Trap

In everyday trade conversation, grease trap is the catch-all term for any device that sits between your kitchen drains and the sewer and separates fats, oils, and grease (FOG) from wastewater before it leaves the building. Council notices, trade waste agreements, and cleaning contractors all tend to use it this way.

The term comes from the original design: a box, usually under the sink or nearby, that traps grease by letting it float to the top while water drains out the bottom. That physical principle has not changed in over a century.

So when your trade waste agreement refers to your grease trap, it means whatever FOG separation device your kitchen has installed, regardless of what the manufacturer printed on the lid.

What a Grease Interceptor Actually Is

A grease interceptor is a specific type of grease trap. It is larger, usually installed underground outside the building, and handles the combined drain load from the whole kitchen. Some councils and water authorities use the term interceptor to describe units above a certain capacity, typically anything over 100 litres in Australia, though the threshold varies by jurisdiction.

The key differences come down to size, location, and how often they need to be pumped.

Size and Location

Under-sink grease traps are small, anywhere from eight to sixty litres for a typical commercial unit. They sit indoors, close to the source, and catch grease from one or two outlets.

Grounded grease interceptors hold hundreds to thousands of litres. They are buried outside the kitchen, often in a car park or service lane, and handle the full discharge from every drain in the building. A large restaurant or hotel kitchen will almost always have one of these.

Pump-Out Frequency

Because small under-sink traps fill quickly, they need to be cleaned more often, sometimes every week or fortnight for a busy kitchen. A large interceptor, because of its volume, may only need pumping every one to three months, depending on kitchen output and local rules.

The Grease Trap Cleaning Blog, Compliance, Costs & Tips | GreaseTrapQuotes covers scheduling in more detail, but the short version is this: frequency is set by your trade waste agreement, not by guesswork.

How Australian and NZ Councils Classify Them

Different water authorities use different language. Sydney Water uses the term grease trap for under-sink devices and grease interceptor for larger below-ground units. Melbourne Water and South East Water both tend to use grease trap as the umbrella term in their trade waste documentation.

In New Zealand, councils and Watercare in Auckland refer to grease interceptors in their trade waste bylaws, but cleaning contractors on the ground will often call them grease traps when talking to a kitchen owner.

The practical point: check what term your trade waste permit uses, then make sure your cleaning records match that language. An inspector looking for grease interceptor pump-out records will not accept a receipt that says under-sink trap, even if it is the same physical device.

The US EPA's FOG management guidance explains the federal-level rationale for FOG control, and the underlying science is the same regardless of what the device is called in your jurisdiction.

Which One Does Your Kitchen Have?

If you are not sure what you have, look for these signs:

• An under-sink box with a removable lid inside the kitchen, that is a grease trap (small unit).
• A concrete or fibreglass access lid set into the ground outside, near the kitchen exit or in a service lane, that is almost certainly a grease interceptor.
• Some kitchens have both: a small under-sink trap that pre-separates grease before it reaches a larger outdoor interceptor.

If you have both, both need to be on your maintenance schedule. Missing one is a common reason kitchens fail trade waste inspections.

Passive vs Automatic Grease Removal

Both grease traps and grease interceptors can be either passive or automatic.

A passive device relies on gravity and retention time. Wastewater sits in the unit long enough for grease to float and be separated. No moving parts. These are the most common type in Australian commercial kitchens.

Automatic Grease Removal Units (AGRUs or AGIs) use a heated scraper or skimmer to continuously remove grease into a separate collection container. They are more expensive to install but can reduce pump-out frequency significantly. Some large volume kitchens use them to stay compliant without weekly contractor visits.

Whether your unit is passive or automatic changes your cleaning schedule and what a contractor needs to do when they arrive. It is worth confirming which type you have before you get a quote, so the contractor prices the job correctly from the start.

Why the Distinction Matters for Compliance

Trade waste agreements are legally binding. They specify the type of device, its capacity, and the maximum pump-out interval. If your device is classified as a grease interceptor on the permit but you are only cleaning an under-sink trap and ignoring the outdoor unit, you are non-compliant, regardless of how clean the indoor trap is.

Water authorities in Australia can issue infringement notices and suspend trade waste agreements for non-compliance. A suspended agreement means you cannot legally discharge kitchen wastewater to the sewer. That is not a theoretical risk. Sydney Water's trade waste section publishes its enforcement approach, and it includes site inspections and penalties for ongoing non-compliance.

Watercare in Auckland takes a similar approach under its trade waste bylaw, with inspections and graduated enforcement.

If you are unsure whether your device is classified correctly on your permit, contact your local water authority and ask them to confirm. It is a short call and the answer protects you.

What to Tell a Cleaning Contractor

When you contact a grease trap cleaning company, give them this information upfront:

• Whether you have an indoor unit, an outdoor unit, or both
• The approximate size or capacity if you know it (often printed on the unit or in your install paperwork)
• What your trade waste permit specifies for pump-out frequency
• Whether it is passive or automatic

A contractor who knows what they are dealing with before they arrive will quote accurately and arrive with the right equipment. A contractor who turns up expecting a small under-sink unit and finds a 2,000-litre underground interceptor will either need to come back or charge you a call-out fee.

The 3 Licensed Grease Trap Quotes in 60 Seconds | GreaseTrapQuotes platform connects you with licensed contractors in your area who can quote on the right scope from the start.

If you have ever thought about cleaning the unit yourself, read Can I Clean a Grease Trap Myself, or Do I Need a Professional? | GreaseTrapQuotes first. The short answer depends on the size and type of device, and on what your trade waste agreement actually allows.

The Quick Summary

Grease trap and grease interceptor describe the same category of device, a FOG separator between your kitchen drains and the sewer. In practice, grease trap usually refers to smaller, indoor, under-sink units. Grease interceptor usually refers to larger, outdoor, below-ground units. Some kitchens have both.

What matters most is what your trade waste agreement says, what device you actually have installed, and whether your pump-out records match both. Get those three things aligned and you will not have a problem when an inspector comes through.

Ready to book a clean or confirm you are on the right schedule? Get 3 Grease Trap Quotes | GreaseTrapQuotes and compare licensed contractors in your area in under a minute.

Related reading: Grease Trap Cleaning Cost in Melbourne: What You're Actually Paying For in 2026.