The everyday difference

In everyday kitchen talk:

  • "Grease trap" usually means a smaller unit inside the building: under a three-compartment sink, in the floor near the dish area, or just outside the kitchen.
  • "Grease interceptor" usually means a large tank, typically buried outside, holding hundreds or thousands of gallons and pumped by a vacuum truck.

Both do the same job. Kitchen wastewater slows down inside the device, fats, oils, and grease (FOG) float to the top, food solids sink, and the clearer water in between flows on to the sewer. The U.S. EPA describes these devices as a way for food service establishments to accumulate grease on-site and keep it out of the public sewer system.

How the technical definitions split it

Engineers and plumbing codes divide interceptors by how they work rather than by name. The Hancock County Utility Authority's 2011 FOG ordinance gives clear definitions that match common usage:

  • Gravity grease interceptor: identified by volume, a 30-minute retention time, baffles, a minimum of two compartments, a minimum total volume of 300 gallons, and gravity separation. It's designed by a registered professional engineer and generally installed outside. This is the big in-ground tank most people mean by "interceptor."
  • Hydromechanical grease interceptor: identified by flow rate and separation and retention efficiency, using air entrainment, hydromechanical separation, interior baffling, and/or barriers, with an external flow control and an air intake (vent). These are the compact units most people call "grease traps."
  • Grease removal device (GRD): a hydromechanical interceptor that removes grease automatically or mechanically.

Do local rules treat them differently?

  • Harrison County (HCUA): HCUA's regulation defines "grease trap" broadly, as any device, fixture, or equipment designed to capture, separate, or collect grease from a generator's discharge. So the permit, 90-day, permitted-hauler, and manifest rules apply whether you call your unit a trap or an interceptor. See the HCUA requirements guide.
  • Hancock County: new food service facilities must design, install, operate, and maintain a grease interceptor under locally adopted plumbing codes, installed and inspected before a certificate of occupancy is issued. Interceptors must be fully evacuated when cleaned, on a 30-day baseline. Only hydromechanical interceptors of no more than 100 GPM may be cleaned by the operator, and only with the Authority's approval and a detailed maintenance log.
  • Jackson County (JCUA retail customers): JCUA's rules (revised March 9, 2026) require Category 2FS food service customers to install a grease trap underground, following EPA design guidance.
  • Ocean Springs: the city's commercial building permit checklist requires grease trap specs for new restaurants, bars, lounges, and night clubs before permitting. See Ocean Springs.

Why the difference matters for service

  • How often. Small indoor units hold little, so a busy kitchen can fill one fast; frequent service, sometimes weekly to monthly, is common. Large interceptors hold more, but the same 25% guideline and local maximums apply. See how often to pump a grease trap.
  • How it's serviced. Interceptors need a vacuum truck parked within hose reach and access to every lid. Indoor traps may mean running a hose through your kitchen, so timing matters. See grease interceptor cleaning and grease trap pumping.
  • What it costs. Size, access, and condition are the biggest price drivers. See what affects grease trap cleaning cost.
  • How problems show up. A full indoor trap tends to cause slow sinks and odors in the kitchen quickly. Interceptor problems can stay hidden underground until a line backs up or an inspection finds grease passing through.

Which one does your kitchen need?

That usually isn't your call alone. Device type and size are set by the plumbing code your city or county has adopted, your sewer authority's rules, and your building's design, often by an engineer. If you're opening or renovating a restaurant, check with your city's building department and your sewer authority before you buy equipment. If you're taking over an existing space:

  1. Ask the previous owner or landlord for past manifests, which usually show the trap size.
  2. Look for lids: small ones inside near sinks, or larger manhole-style covers outside.
  3. Check the building's plumbing plans if you have them.
  4. Still not sure? Choose "Not sure" on our quote form and a provider can locate and measure it on the first visit.

One rule for both: skip the additives

Enzymes, soaps, and degreasers sold to "dissolve" grease often just push it further down the line, where it hardens in the sewer. Hancock County's ordinance prohibits surfactants, solvents, and emulsifiers in grease interceptors, naming enzymes, soap, diesel, kerosene, and terpene. Wherever you are on the Coast, ask your provider before putting any product into your trap.