How Grease Traps and Grease Interceptors Work
If you own or manage a restaurant, cafeteria, hotel kitchen, or any other food-service operation, you already know that what goes down the drain matters. Every fryer basket, sauté pan, and dish rack sends fats, oils, and grease, known in the industry as FOG, toward your plumbing. When that FOG cools, it hardens, sticks to pipe walls, and eventually chokes off drainage entirely.
That’s why every commercial kitchen is required to have a grease control device in place. But there’s often confusion about the two main options: grease traps and grease interceptors. They sound interchangeable, and many people use the terms that way, but they’re built for very different kitchens and very different workloads.
In this article, the team at Citywide Sewer-Drain & Plumbing breaks down how each device works, which one your kitchen likely needs, how often it should be serviced, and what can happen when maintenance falls behind.
Why FOG Is a Problem in the First Place
Grease doesn’t stay liquid for long once it leaves a hot pan. As wastewater travels through your drain lines, it cools, and the FOG separates and clings to the inside of the pipe. Over weeks and months, that layer thickens until water can barely pass through.
The problem doesn’t stop at your property line, either. Grease that reaches the municipal sewer contributes to blockages that cause sewage overflows into streets and waterways. That’s why cities and counties enforce FOG ordinances that require food-service businesses to capture grease before it enters the public system, and why inspectors take those rules seriously.
What Is a Grease Trap?
A grease trap is a small, passive device usually installed under or near a kitchen sink, dishwasher, or prep station. Most hold somewhere between 20 and 50 gallons and are made of steel or heavy-duty plastic.
Here’s how it works: wastewater flows into the trap and slows down. As it sits, the grease and oil, which are lighter than water, float to the top, while food particles settle to the bottom. The relatively clean water in the middle continues on to the drain line.
Grease traps are a good fit for:
- Coffee shops and bakeries
- Small cafés and sandwich shops
- Food trucks and concession stands
- Kitchens with light to moderate grease output
Because they hold so little, grease traps fill up fast. Many local codes require them to be cleaned every 30 days or whenever they reach 25 percent capacity, whichever comes first. Skip a cleaning, and you’ll notice it quickly: slow sinks, gurgling drains, and a sour smell that carries into the dining room.
What Is a Grease Interceptor?
A grease interceptor does the same job on a much larger scale. These units are typically buried outside the building or installed in a below-grade vault, and they can hold anywhere from 500 to several thousand gallons. Rather than serving a single sink, an interceptor collects wastewater from every fixture in the kitchen, including prep sinks, three-compartment sinks, mop sinks, dishwashers, and floor drains.
Cross-section of a grease interceptor: wastewater flows in, grease floats to the top, solids settle below the baffle wall, and clarified water flows out to the sewer.
Inside, a series of baffles slows the water down and gives grease plenty of time to separate. Because the capacity is so large, interceptors don’t need to be emptied nearly as often as indoor traps. When they do, though, it’s not a job for a bucket and a scraper. Servicing an interceptor requires a vacuum truck, proper disposal of the pumped waste, and a technician who knows how to inspect the baffles, inlet, and outlet for damage.
Grease interceptors are the right choice for:
- Full-service and high-volume restaurants
- Hotels and banquet facilities
- Hospitals, schools, and institutional kitchens
- Any operation with multiple fryers or heavy grease production
Most jurisdictions require interceptors to be pumped at least every 90 days, though busy kitchens may need it more often.
Grease Trap vs. Grease Interceptor at a Glance
What Happens When Maintenance Slips
It’s easy to push grease service to the bottom of the to-do list, especially during a busy season. Unfortunately, a neglected grease device rarely fails quietly. Here’s what kitchens typically run into:
Backups and shutdowns. Once the trap or interceptor is full, grease passes straight through into the drain line. A clog there can back up floor drains and sinks in the middle of service, and a health inspector will close the kitchen until it’s resolved.
Persistent odors. Rancid grease has a distinctive smell, and it doesn’t stay in the back of the house. Customers notice, staff complain, and online reviews follow.
Code violations and fines. Most municipalities inspect grease devices and require cleaning records. Failing an inspection can mean daily fines, mandatory emergency pumping at premium rates, and a paper trail that follows your business.
Expensive repairs. Hardened grease is far more difficult to remove than fresh grease. What could have been a routine cleaning can turn into hydro-jetting, line replacement, or even excavation.
Safety hazards. Overflowing traps create slick floors, and grease buildup near cooking equipment raises fire risk.
How Often Should You Service Your System?
There’s no single answer, because the right schedule depends on your menu, your volume, the size of your device, and your local ordinance. A steakhouse with four fryers will fill an interceptor much faster than a salad bar. That said, a few rules of thumb apply:
- Indoor grease traps: every 30 days, or sooner if the trap reaches a quarter full
- Outdoor grease interceptors: every 90 days at minimum
- Any device: immediately if you notice slow drains, odors, or visible grease at the outlet
Keeping a written maintenance log is also a good idea, and in many areas it’s required. Inspectors will want to see dates, the company that performed the service, and how much material was removed.
How Citywide Sewer-Drain & Plumbing Can Help
Citywide Sewer-Drain & Plumbing works with restaurants and commercial kitchens to keep grease systems running properly and inspection-ready. Our commercial plumbing services include:
Grease trap and interceptor installation. Not sure which device your kitchen needs, or whether your current one is properly sized? We’ll evaluate your fixtures, flow rate, and local code requirements and install the right solution.
Scheduled cleaning and pumping. We’ll set up a maintenance schedule that matches your volume and your municipality’s rules so you never miss a service window.
Repairs and inspections. Damaged baffles, corroded tanks, and failed seals all reduce a device’s effectiveness. We diagnose and repair problems before they become violations.
Drain cleaning and hydro-jetting. If grease has already made its way into your lines, we clear it out and restore full flow.
Emergency service. Backups don’t wait for a convenient time. When your kitchen is down, we respond quickly to get you back in business.
Keep Your Kitchen Flowing
Grease traps and grease interceptors aren’t glamorous, but they’re one of the most important pieces of equipment in any commercial kitchen. Choosing the right device and keeping it on a regular service schedule protects your plumbing, keeps inspectors satisfied, and lets you focus on running your business.
Whether you need a new installation, routine maintenance, or help with a backup right now, contact Citywide Sewer-Drain & Plumbing today to schedule your commercial grease service.
Citywide Sewer-Drain Plumbing Service Corp has been serving Long Island, Queens, Brooklyn, and all five NYC boroughs for over 65 years. Our licensed technicians can inspect, repair, or replace your grease trap or grease interceptor.
📞 Schedule a grease trap service today 1-800-310-2564