Grease Trap Maintenance: What Restaurants Need to Know

Every commercial kitchen sends fats, oils, and grease down the drain. A grease trap or grease interceptor is what keeps that grease from reaching the sewer, where it hardens and causes blockages. When the trap is neglected, the backup usually shows up in your own kitchen first — often during a dinner rush. Here is what restaurant owners and managers should know.

Trap or interceptor — what's the difference?

A grease trap is typically a smaller unit installed inside the building, often under or near a sink. A grease interceptor is usually a much larger tank, frequently buried outside. Both do the same job: they slow wastewater down so grease floats to the top and solids settle to the bottom, letting cleaner water continue to the sewer. The type and size you need is set by local code and your kitchen's volume.

How often does it need attention?

It depends on the size of the unit and how much grease your kitchen produces. A common rule of thumb is to clean the unit before grease and solids fill about a quarter of its depth. Small indoor traps in a busy kitchen may need attention every few weeks. Large outdoor interceptors are often pumped every one to three months. Your local sewer authority may set its own schedule and require records, so check your permit or ask them.

Warning signs of a problem

• Slow-draining sinks or floor drains in the kitchen
• Strong, sour odors near drains or the trap lid
• Water backing up into floor sinks
• Grease visible in downstream cleanouts or manholes
• A notice from your sewer authority or health inspector

Why regular service matters

Skipping maintenance costs more than the service itself. A full trap lets grease pass into your building drain, where it builds up and eventually blocks the line. Clearing a grease-packed drain, cleaning up a backup, and losing a day or more of business can far exceed the cost of routine pumping. Sewer authorities can also issue violations or fines when grease from a property causes problems in public lines.

Kitchen habits that help

• Scrape plates and pans into the trash before washing
• Collect fryer oil in a recycling container — never pour it down a drain
• Use sink strainers and empty them often
• Avoid very hot water and harsh chemicals meant to 'dissolve' grease; they move it downstream where it hardens
• Keep a maintenance log with dates and who performed the service

When the drain lines need more than pumping

Pumping empties the trap, but it does not clean the drain lines leading to it. If you keep having backups after the trap is serviced, a camera inspection can show whether grease buildup, a sag in the line, or damaged pipe is the real cause. Older buildings are sometimes found to have undersized or missing grease protection entirely.

Planning a new kitchen or remodel?

Grease interceptor sizing and placement should be settled early in design. Legacy Plumbing installs, repairs, and replaces grease interceptors and kitchen drainage for restaurants and food service across the St. Louis metro. Request service for an inspection, or send us your plans for a bid.