Every commercial kitchen produces fats, oils and grease (FOG) as a by-product of cooking, food preparation and dishwashing. Left unmanaged, FOG hardens inside pipes, chokes drainage systems and contributes to the notorious fatbergs that block municipal sewers. The two devices designed to stop this from happening are the grease trap and the grease interceptor. Both perform the same essential job, yet they differ in size, capacity, installation and maintenance requirements. Understanding the grease trap vs grease interceptor debate will help you choose the right system for your establishment and keep your kitchen compliant, hygienic and free of costly blockages.
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What Is a Grease Trap?
A grease trap is a compact plumbing device that separates fats, oils and grease from wastewater before it enters the drainage system. The technology dates back to the 1880s, and remarkably little about the basic design has changed since then, largely because it works so well.
How a Grease Trap Works
When wastewater drains from a sink or dishwashing station, it flows into the trap and slows down. As the water cools, the FOG solidifies and rises to the surface, while heavier food particles sink to the bottom as sludge. A series of baffles encourages this separation, leaving the cleaner water in the middle of the tank to continue on to the sewer or septic system. The captured grease accumulates from the top down until the unit is emptied.
Size and Location
Grease traps are small units, typically comparable to a shoebox, microwave or bar fridge depending on the model, with capacities generally ranging from about 40 to 170 litres. Because of their compact footprint, they are usually installed above ground, directly beneath the kitchen sink or as close as possible to the source of grease production. This makes them quick to install and easy for staff to access.
Who Uses Grease Traps?
Grease traps suit kitchens with lower volumes of wastewater, generally those with flow rates below roughly 190 litres (50 gallons) per minute. Cafés, coffee shops, bakeries, takeaways, small restaurants, office canteens and school kitchens all typically rely on under-sink grease traps to manage their FOG output.
What Is a Grease Interceptor?
A grease interceptor is best thought of as a grease trap operating at a much larger scale. It performs exactly the same separation process, but it is engineered to handle the heavy wastewater flows produced by busy, high-volume kitchens.
How a Grease Interceptor Works
Wastewater from multiple kitchen sources, including sinks, dishwashers and floor drains, enters the interceptor tank, where the flow slows dramatically. Gravity does the rest: grease floats to the top, solids settle at the bottom, and the clarified water in between discharges to the municipal sewer or, on properties without sewer access, to a wastewater storage tank.
Size and Location
Grease interceptors are substantial installations, with capacities starting at around 1,000 litres and dimensions often measured in metres rather than centimetres. Because of their bulk, they are almost always installed outside the building, usually buried underground between the kitchen’s drainage system and the main sewer line. This external placement keeps odours away from customers and staff and gives service teams easy access for pumping and cleaning.
Who Uses Grease Interceptors?
Any operation with a wastewater flow rate above roughly 190 litres per minute will need an interceptor. That includes hotels, hospitals, shopping centres, large restaurants, fast-food chains, industrial kitchens and food processing facilities. Some very busy establishments run both systems, with traps at individual prep sinks and an interceptor handling the main kitchen flow.
Grease Trap vs Grease Interceptor: The Key Differences
Although the two devices share the same purpose and working principle, several practical differences determine which one belongs in your kitchen.
Capacity and Flow Rate
Capacity is the clearest dividing line. A grease trap handles low-pressure, low-volume flows and holds a relatively modest amount of FOG, while an interceptor is built for high-pressure environments and can retain hundreds or thousands of litres of grease between services. If your kitchen runs multiple wash stations, deep fryers and commercial dishwashers simultaneously, a trap alone simply cannot keep up.
Installation
A grease trap slots neatly under a sink and connects to the smaller internal plumbing, making installation fast and non-disruptive. A grease interceptor requires excavation, external space and a connection to the main sewer line, which means a longer, more involved installation process, and in most municipalities, approval from the local authority before work begins.
Materials
Grease traps are commonly manufactured from stainless steel, mild steel, plastic, PVC or fibreglass. Interceptors must withstand far greater volumes, higher flow rates and the surrounding soil conditions, so concrete becomes a common construction material alongside heavy-duty steel and fibreglass.
Cleaning and Maintenance
A grease trap fills quickly because of its small capacity, so it needs frequent attention. Staff can empty and wipe down smaller units daily or weekly, with professional cleaning recommended at least monthly. A useful rule of thumb is to service the trap once FOG and solids occupy a quarter of its capacity, as efficiency drops sharply beyond that point. Grease interceptors, thanks to their far larger holding capacity, can generally go around three months between services, but their size and underground placement mean they must be pumped out by a professional team with a vacuum tanker rather than emptied by hand.
A Note on Terminology
You may notice that modern plumbing standards are moving away from the phrase “grease trap” altogether. Under newer classifications, both devices fall under the umbrella of grease interceptors: the compact under-sink unit is technically a hydromechanical grease interceptor, which uses baffles and flow control to separate grease quickly, while the large in-ground tank is a gravity grease interceptor, which relies on longer retention times. You may also hear the term “grease arrestor”, which is simply another name for a grease trap. Whatever the label, the separation science is identical, so focus on capacity and flow rate rather than terminology when comparing systems.
Why Proper Grease Management Matters
Wastewater treatment plants cannot process grease, and FOG that escapes into the sewer congeals into stubborn blockages. It is estimated that the vast majority of sewer blockages are caused by grease build-up, and the resulting backups can flood a kitchen with raw sewage, force temporary closure and land the business with steep municipal fines and repair bills. A correctly sized, well-maintained trap or interceptor protects your internal plumbing, keeps your establishment compliant with local by-laws and prevents environmental contamination, all for a fraction of what emergency call-outs and pipe replacements cost.
Choosing the Right System for Your Kitchen
The decision ultimately comes down to scale. A small kitchen with a single wash-up station and a modest menu will be well served by an under-sink grease trap, cleaned regularly and professionally serviced on schedule. A high-volume operation with multiple sinks, fryers and dishwashers needs the capacity of an underground grease interceptor, professionally pumped at least quarterly. If you are unsure where your kitchen falls, a drainage professional can assess your flow rate, review your local municipal requirements and recommend the correct size and type of system, so your grease stays where it belongs and your drains keep flowing freely.
