Grease Traps for Kitchens: How to Size, Select and Maintain One

A grease trap, also called a grease interceptor, catches fats, oils and grease before they enter the sewer line, preventing clogs and helping you meet local regulations. The right model depends on your flow rate, the fixtures it serves, local code requirements and where it will be installed. Because rules vary by municipality, confirm requirements with your local authority before you buy.

What a Grease Trap Does

Wastewater from sinks and dishwashers flows into the trap, where it slows down and cools. Grease, being lighter than water, rises and collects at the top, while solids settle and the cleaner water flows out. The trap must be emptied and cleaned regularly. Without maintenance, it overflows or stops working, leading to odors, backups and fines. Commercial kitchens are typically required to have one; some homes and small businesses use smaller units under sinks.

Passive Versus Automatic Models

Passive traps rely on gravity and require manual cleaning. They are common in restaurants and under-sink installations because they are simple and relatively inexpensive. Automatic grease removal units skim grease from the surface and store it in a container, reducing manual cleaning. Large in-ground concrete interceptors serve high volumes and are usually installed outside by professionals. Choose based on the amount of grease, labor available and regulations.

• Passive under-sink: low cost, manual cleaning.
• Automatic skimming: less labor, higher cost.
• In-ground interceptor: large capacity, professional installation.
• Portable units: for food trucks and events, where permitted.

Sizing: Flow Rate and Capacity

Two numbers matter: the flow rate, which is how much water passes through per minute, and the grease capacity, which is how much grease the trap holds before it needs cleaning. Flow rate is based on the fixtures it serves, such as sinks and dishwashers, and their drain rates. Capacity influences the cleaning interval. An undersized trap clogs quickly and may not meet code. Many jurisdictions have sizing formulas, so consult local plumbing code or a licensed plumber.

Type Comparison

Materials, Features and Certification

Common materials include stainless steel, polyethylene and cast iron or concrete for larger units. Stainless steel is durable and easy to clean, while plastic resists corrosion and is lighter. Look for removable baffles, easy-access lids, gasketed covers to reduce odor and flow-control fittings. Check for compliance with applicable standards, which may include performance testing from recognized bodies. Many municipalities require approved models, so ask your local plumbing or wastewater authority.

Installation should follow code, including venting, air gaps and access for cleaning. A licensed plumber is advisable, particularly for commercial installations and any work that affects public sewer connections.

Cleaning Schedule and Practical Habits

Maintenance is the heart of grease trap performance. Many facilities clean when grease and solids reach a set fraction of the trap volume, often a quarter of capacity, but follow local rules. Keep a log of cleanings and disposal. Never dump collected grease down drains; use licensed haulers or approved recycling programs. Scrape plates before washing, use sink strainers and avoid pouring fryer oil down drains. These habits reduce load on the trap and extend cleaning intervals.

Wear gloves and eye protection during cleaning, ventilate the area and be careful with slippery surfaces. Grease traps can produce unpleasant and potentially hazardous gases, so avoid entering confined spaces.

Shopping Guide

If you are comparing smaller units, browse commercial kitchen grease traps and check flow rate and capacity. For under-sink models, see under-sink grease traps. Cleaning tools such as grease trap cleaning supplies make the job easier and safer.

Mistakes to Avoid

The common mistakes are buying without checking local code, undersizing, putting off cleaning, adding a trap to a line it was not designed for and disposing of grease improperly. Another mistake is ignoring the connected fixtures: dishwashers discharge hot water that can reduce separation efficiency, so follow manufacturer and code guidance.

Working With Inspectors and Haulers

Many municipalities inspect grease traps and expect cleaning records. Keep manifests from licensed haulers, note the date and volume removed and store them where inspectors can find them. If you are opening a new kitchen, ask the local sewer or health department about plan review, approved models and sizing before you purchase anything. This conversation can save you from buying a trap that fails inspection.

Reducing Grease at the Source

The most economical strategy is less grease in the drain. Train staff to scrape and wipe pans, collect used cooking oil in separate containers and avoid garbage disposals that push more solids into the trap. Fit drain screens, run hot water sparingly and use enzyme or bacterial products only if they are permitted locally, since some codes restrict additives that emulsify grease.

Frequently Asked Questions

Do I need a grease trap at home?

Usually not, but some homeowners add a small unit for heavy cooking. Check local rules.

How often should it be cleaned?

It depends on use and local rules. Frequent cleaning prevents odors and overflows.

Can I install it myself?

Small under-sink models may be a DIY job in some places, but commercial installations typically need a licensed plumber and permits.