You have perfected the menu, hired the staff, and designed the dining room. But before you can serve a single customer, you have to pass the plumbing inspection.

For 90% of new restaurants, the biggest hurdle is the Grease Trap (technically called a Grease Interceptor).

City municipalities are cracking down harder than ever on FOG (Fats, Oils, and Grease). If your kitchen sends grease into the city sewer, you face massive fines, pipe-cleaning charges, and even immediate closure.

Here is the no-nonsense guide to understanding what you need, how to size it, and how to maintain it in 2026.

1. What is a Grease Trap and Why Do I Need It?

When hot grease (from fryers, dishwashers, and woks) goes down the drain, it cools and solidifies. If it enters the city sewer, it combines with debris to form "Fatbergs" that block main lines.

A grease trap is a plumbing device that slows down the wastewater, allowing the oil to float to the top and solids to sink to the bottom. The cleaner water in the middle then exits to the sewer.

The Law: Virtually every municipality requires a grease interception device for any facility preparing food. This includes coffee shops with dairy, bakeries, and full-service restaurants.

2. The Two Main Types: Which One Do You Need?

A. Hydro-Mechanical Interceptors (The "Under-Sink" Trap)

Location: Usually installed indoors, directly under the 3-compartment sink or in the floor.
Material: Steel or plastic.
Best For: Small cafes, delis, or kitchens with low grease output.
Pros: Cheaper to install.
Cons: Fills up very fast; requires frequent cleaning (sometimes weekly).

B. Gravity Grease Interceptors (The "Big Tank")

Location: Buried underground outside the building.
Capacity: 500 to 2,000+ gallons.
Best For: Full-service restaurants, fast food chains, and heavy grease producers.
Pros: Can go months without pumping; handles high flow.
Cons: Expensive installation (requires excavation).

3. Sizing: The Most Critical Step

You cannot just buy a random trap at a hardware store. Your trap must be sized according to the Plumbing and Drainage Institute (PDI) standards.

If you undersize it, you will fail inspection. If you oversize it, you waste money.

The Calculation (Simplified): Plumbers calculate the GPM (Gallons Per Minute) of your fixtures.

Calculate Volume: Length x Width x Depth of your sinks.
Determine Flow Rate: Based on how fast the sinks drain.
Match to PDI Rating: If your sink drains 20 gallons per minute, you generally need a 40-pound trap.

Note: Always consult a licensed commercial plumber for this. One wrong calculation can require ripping out concrete later.

4. The "25% Rule" (Maintenance)

This is the rule most new owners break. A grease trap is considered "full" when it reaches 25% capacity of grease and solids.

It does not need to be 100% full to fail. Once the grease layer covers 25% of the tank depth, the trap loses efficiency and starts letting grease escape into the sewer.

Indoor Traps: Usually need cleaning monthly (or weekly).
Outdoor Tanks: Usually need pumping quarterly (every 3 months).

Documentation is Mandatory: You must keep a "FOG Log" (maintenance log). City inspectors can drop in unannounced and ask to see your cleaning records. If you can't prove you pumped it, you get fined.

5. Best Practices for Your Staff

The best grease trap is a clean kitchen culture. Train your staff on these three rules:

"Dry Wipe" Everything: Scrape plates and pans into the trash before putting them in the sink.
No Oil in Drains: Never pour fryer oil down the sink. It must go in a rendering bin.
Use Strainers: Keep sink strainers in place to catch food solids.

Conclusion

In the restaurant business, plumbing problems are revenue killers. A backed-up grease trap smells horrific, drives away customers, and can shut your kitchen down on a Friday night.

Do it right the first time. Size it correctly, install it professionally, and schedule your maintenance before you open the doors.

Opening a new restaurant? Contact our Commercial Division for PDI-certified sizing and installation.

Sources & Further Reading

For official standards and maintenance guidelines regarding commercial grease interceptors, please refer to: