What Is a Grease Trap and How It Works

Grease traps. You’ve probably heard the term before, especially if you’ve ever worked in a commercial kitchen or own a restaurant. But what is a grease trap, really? Is it just another plumbing thing, or is there more to it than meets the eye? Whether you’re a business owner, property manager, or just a curious reader trying to figure out how restaurants deal with all that kitchen waste, this article breaks it all down in simple, straightforward terms.

What Is a Grease Trap?

Let’s start with the basics. A grease trap, also known as a grease interceptor, is a plumbing device designed to capture fats, oils, and grease (commonly called FOG) before they enter the main sewer system. These substances don’t mix well with water and can cause major clogs when they build up in pipes.

Grease traps have been around for over a hundred years. They were first patented in the late 1800s, and while the materials and designs have evolved, the core idea hasn’t changed much. Keep the grease out of the sewer and prevent plumbing disasters. That’s the name of the game.

Why Are Grease Traps Important?

Imagine this. You run a diner, and every day, your kitchen produces a fair amount of grease. Bacon grease, fryer oil, leftover butter, these things don’t just vanish down the sink. If they enter your plumbing system unchecked, they can solidify, stick to the pipes, and eventually cause backups, overflows, or even full-blown sewer blockages.

Not only is that a nightmare for your business, but it can also lead to health violations and fines. In many cities and towns, grease traps are legally required for commercial kitchens and food establishments. Municipal wastewater systems simply can’t handle the volume of grease that comes from food service locations.

How Does a Grease Trap Work?

So how does this humble little device actually work? Well, a grease trap operates using a fairly simple principle: grease floats and solids sink.

Here’s a quick breakdown of the process:

1. Kitchen wastewater enters the grease trap through a connected pipe.

2. Inside the trap, the flow of water slows down. This gives time for separation to occur.

3. Grease, fats, and oils, being lighter than water, rise to the top.

4. Solids and food particles settle at the bottom.

5. The cleaner, cooler water exits through an outlet pipe into the main sewer system.

What’s left behind is a layer of scum on top (the grease) and sludge on the bottom (the solids). Over time, both layers build up and need to be pumped out. That’s why regular grease trap maintenance is essential—a neglected trap won’t function properly and can cause worse problems than if you didn’t have one at all.

Types of Grease Traps

Grease traps come in different shapes, sizes, and setups. The type you need depends on your kitchen’s volume and setup.

1. Passive Hydromechanical Grease Traps (Small Traps)

These are small units usually located under a sink or in the kitchen floor. They’re made of metal or plastic and can handle low to medium volumes of grease. They’re popular in small restaurants or food trucks.

2. Gravity Grease Interceptors (Large Outdoor Traps)

These are larger tanks made of concrete, fiberglass, or steel, usually installed underground outside the building. They use gravity to slow down water flow and separate the grease, much like a septic system. These are more suitable for high-capacity kitchens, like hotels or large restaurants.

3. Automatic Grease Removal Units (AGRU)

These are more high-tech versions that remove grease automatically using mechanical parts. They’re efficient but more expensive, so they’re typically used in places where hygiene standards are strict, or where maintenance needs to be automated.

Where Are Grease Traps Installed?

Good question. It depends.

• Small units are usually installed indoors, under sinks or behind dishwashers.

• Large gravity units are installed outdoors, between the kitchen and the main sewer line.

• Some newer commercial kitchens may have a centralized grease trap system built right into the floor drains and plumbing layout.

Regardless of location, the main goal is to intercept the grease before it can do any damage.

How Often Should a Grease Trap Be Cleaned?

It’s not a “set it and forget it” situation. Grease traps require routine cleaning and inspection to keep working properly. The general rule is the 25% rule—if the trap is 25% full of grease and solids, it’s time for a clean-out.

Cleaning frequency depends on:

• The size of the trap

• The amount of food you produce

• Local laws and regulations

Some places may need cleaning once a month, others every 3 months, but skipping it for too long is asking for a problem.

If your trap starts to smell, back up, or drain slowly, it’s probably overdue.

What Happens If You Don’t Use a Grease Trap?

If you’re wondering, "Can’t I just skip the whole grease trap thing?" the answer is... not unless you want to risk fines, plumbing issues, or a visit from the health department.

Grease buildup can:

• Block sewer lines

• Cause overflows and backups

• Damage your own plumbing and that of nearby buildings

• Attract pests and cause bad smells

• Violate environmental laws

Basically, it’s not worth the risk. Grease traps are a small investment compared to the potential cost of fixing a major plumbing issue—or shutting your business down due to violations.

Grease Trap Regulations

Many local governments have grease trap ordinances in place. These regulations may include:

• How big your trap has to be

• How often it needs to be cleaned

• What kind of records you have to keep

• Whether you need to use a licensed hauler to dispose of the waste

Failing to follow these rules can result in fines or even losing your operating license.

Who Maintains Grease Traps?

Some businesses choose to clean small traps themselves, but most commercial kitchens hire professional grease trap cleaning companies. These companies:

• Pump out the contents

• Haul away the waste to an approved facility

• Clean the interior and check for any damage

• Provide documentation for compliance records

They also know the local regulations and can help you stay in good standing with the city.

Can Grease Trap Waste Be Recycled?

Surprisingly, yes. The FOG collected from grease traps can sometimes be turned into biodiesel, compost, or even methane gas through anaerobic digestion. This process helps reduce the environmental impact of waste grease. Not all companies recycle grease trap waste, but the trend is growing as more people look for sustainable waste solutions.

Final Thoughts

So, what is a grease trap? It’s more than just a box full of kitchen gunk—it’s an essential piece of equipment for protecting your plumbing, your business, and your community’s sewer system. Understanding how it works and keeping it well-maintained will save you a lot of money and hassle in the long run.

Whether you’re just starting a food business or already operating one, don’t overlook the importance of your grease trap. It’s doing a dirty job so you don’t have to.