Fats, oils and grease poured down a kitchen drain cool, harden and stick to pipes. Over time they block the building drain and the city sewer. That is why most cities require commercial kitchens to catch grease before it leaves the building. The device that does this is a grease trap, also called a grease interceptor. This guide explains how grease traps work, how they are usually installed and what to plan for.
Shop the equipment in this article: GT-50 heavy-duty 50 lb grease trap, GT-70 heavy-duty 70 lb grease trap and GT-100 heavy-duty 100 lb grease trap. Freight is included on every order.
How a Grease Trap Works
Wastewater from sinks flows into the trap. Inside, baffles slow the water down. Grease is lighter than water, so it floats to the top and stays in the trap. Solids sink to the bottom. Cleaner water flows out the other side to the sewer. The trap has to be cleaned out on a schedule, or grease fills it and passes through.
What Generally Drains to a Grease Trap
- Three compartment dish sinks.
- Prep sinks and pot sinks.
- Mop sinks in many areas.
- Floor drains and floor sinks in cooking areas, depending on local rules.
Some fixtures are often kept off the grease trap, such as hand sinks and restroom fixtures. Your local plumbing code and sewer authority decide what must connect. Always confirm with them.
Sizing
Traps are sized by flow rate, usually in gallons per minute, and grease capacity in pounds. Your plumber calculates the required size from the number and size of sinks connected and how fast they drain. Your city may have its own sizing method.
- We carry a range of sizes, including:
- GT-50 heavy-duty 50 lb grease trap
- GT-70 heavy-duty 70 lb grease trap
- GT-100 heavy-duty 100 lb grease trap
Low profile units help when there is not much height under a sink, such as the GT-40-LO 40 lbs low profile steel grease trap interceptor and the GT-70-LO 70 lb low profile steel grease trap.
Where to Put It
Under or next to the sink it serves, in the floor, or outside in the ground for large in-ground interceptors. Small and medium traps usually sit on the floor near the dish sink or are set into the floor with the lid flush. Leave clear access to the lid. A trap you cannot reach does not get cleaned.
Typical Install Planning
A licensed plumber should install the grease trap, and the work should be checked against local code. Most installs include:
- A flow control device on the inlet side, which limits flow so the trap has time to separate grease.
- A proper vent so the trap drains correctly and does not siphon.
- Inlet and outlet pipes sized to match the trap connections.
- A level base so the baffles work as designed.
- Access for pumping or manual cleaning.
Many sewer authorities require a permit and an inspection for a new trap. Some require a specific type or a minimum size regardless of your calculation.
Cleaning and Maintenance
Small indoor traps are often cleaned weekly or more in busy kitchens. Larger interceptors are pumped by a licensed hauler on a set schedule. A common rule used by many sewer authorities is to clean the trap before grease and solids fill about a quarter of its depth, but your local rule governs.
Keep a cleaning log. Many cities ask to see it during inspections.
Habits That Protect the Trap
- Scrape plates into the trash before rinsing.
- Pour used fryer oil into a rendering container, never down the drain.
- Wipe greasy pans with a paper towel before washing.
- Use drain strainers in every sink.
- Do not use very hot water or enzymes to push grease through. It just moves the problem downstream.
Next Steps
List every sink that will drain to the trap, then browse our grease traps and review sizes with your plumber. If you are also choosing a dish sink, see our 3 compartment sinks. Questions? Contact Express KitchQuip and we will help you pick the right size and configuration.