Grease trap vs. grease interceptor: what's the difference?
By Stew Israil, GreaseTrapRules · Updated Oct 18, 2026 · Every rule below links to its official source. Rules change; verify with your city.
Short answer: in plumbing codes they are both grease interceptors. "Grease trap" usually means a small hydromechanical unit under or near the sink, rated in gallons per minute. "Grease interceptor" usually means a large gravity tank, often in the ground outside, holding hundreds or thousands of gallons. Which one you need, and how often it must be pumped, is set by your city or sewer utility.
| Hydromechanical ("grease trap") | Gravity ("grease interceptor") | |
|---|---|---|
| Code definition | Intercepts free-floating FOG; continuous separation by air entrainment, buoyancy and interior baffling. | At least 500 gallons; separation by gravity during a retention time of at least 30 minutes. |
| Rated by | Flow (gpm), e.g. 20–100 gpm; grease capacity in pounds (2 lb per rated gpm under IPC Table 1003.3.5.1) | Liquid capacity in gallons |
| Usual location | Under the sink or in the floor, inside | In the ground, outside the building |
| Sized by | PDI-G101 / ASME A112.14.3 sink method | UPC drainage fixture units, IPC peak flow × 30 minutes, or a city formula |
| Typical pumping rule | Weekly to monthly (city examples below) | Often every 90 days or before 25% full |
Definitions: 2021 IPC and UPC, as summarized by the ICC (ICC, 2021 IPC and UPC Essentials (definitions, IPC 1003.3.2 and 1003.3.3)). Some local codes differ: New York City's version of the code puts the gravity minimum at 300 gallons (New York City Plumbing Code definition of grease interceptor (UpCodes)).
How cities draw the line
- Tampa, FL defines a gravity grease interceptor as one rated over 50 gpm or holding 750 gallons or more, underground and outside; a grease trap is rated 50 gpm or less, inside or under a sink (City of Tampa, Grease Trap Definitions).
- Austin, TX says hydromechanical interceptors are generally suited to low-grease businesses such as small sandwich shops, coffee shops and bakeries that use disposable flatware and no dishwasher; kitchens with a dishwasher need at least a 500-gallon interceptor (Austin Water, Grease Trap Sizing & Design Criteria).
- Springfield, IL sets a 35-gallon minimum for grease traps and 500 gallons for interceptors.
- Joliet, IL requires hydromechanical interceptors in all new food service establishments.
Why the pumping rules differ
A small trap fills fast, so cities give it a short leash: Joliet, IL requires grease traps to be cleaned weekly and interceptors every 90 days; Elgin, IL monthly for traps and 90 days for interceptors; Jacksonville, FL (JEA) every two weeks for traps under 50 gallons. More in how often to pump a grease trap.
Things both types can't take
- Garbage disposals. The IPC says food waste disposers shall not discharge to a grease interceptor; Austin, TX has banned disposals in commercial kitchens since 2008.
- Enzymes and emulsifiers. Prohibited under IPC 1003.3.3 and by many cities, including Seattle, WA and Austin, TX.
Minimum sizes cities set
| City | Sizing rule, from the official source |
|---|---|
| Austin, TX | Flow rating = total fixture units × 3 gpm; minimum liquid holding capacity = flow rating × 12 minutes. Traps under 100 gallons are not approved, and kitchens with a dishwasher need at least a 500-gallon interceptor. ✓ hand-checked |
| Cincinnati, OH | Minimum 1,000-gallon gravity grease interceptor for each 950 lbs of grease capacity required. quoted from source |
| Decatur, IL | Interceptors thus located shall have a minimum capacity of 1,000 gallons. quoted from source |
| Elgin, IL | In general FRWRD requires outside, 1,000-gallon minimum traps for all food service establishments; existing businesses changing ownership, renovating or expanding must meet the 1,000-gallon outside standard. ✓ hand-checked |
| Fox Lake, IL | (Sandwich bars and carryout services, which only prepare noncooked foods such as cold sandwiches, shall install a minimum 400 gallon grease interceptor unless the director of the POTW grants a variance.). quoted from source |
| Greensboro, NC | An exterior grease interceptor has a minimum capacity of 1,000 gallons; under-counter grease traps are usually limited to four fixtures and 50 gallons per minute combined. ✓ hand-checked |
| Los Angeles, CA | LASAN defines a grease interceptor as a device with a minimum size of 750 gallons. ✓ hand-checked |
| New Orleans, LA | Traps are typically in- floor recessed grease retention units, which are normally not less than 125 gallons capacity. quoted from source |
| Peoria, IL | Commercial buildings expected to generate significant FOG (as determined by GPSD) must install a grease interceptor of at least 250 gallons; restaurants generating large quantities of FOG must install at least 1,000 gallons. ✓ hand-checked |
| Rockford, IL | New or altered food service establishments that discharge FOG in quantities large enough to block lines must install a minimum 1,000-gallon interceptor; strip-mall interceptors may be no less than 1,500 gallons. ✓ hand-checked |
| Springfield, IL | Grease traps: minimum 35 gallons; grease interceptors: minimum 500 gallons (variance possible for traps). New building construction requires a minimum 500-gallon interceptor. ✓ hand-checked |
| Winston-Salem, NC | New in-ground grease interceptors must be at least 1,000 gallons total capacity unless the Director approves otherwise, sized for a 24-minute retention time at actual peak flow. ✓ hand-checked |
FAQ
Is a grease trap the same as a grease interceptor?
In plumbing codes, both are grease interceptors. People usually say "grease trap" for a small hydromechanical unit under or near the sink and "grease interceptor" for a large gravity tank, often buried outside. Some cities define them by size: Tampa calls anything rated 50 gpm or less, inside or under a sink, a grease trap.
What is a hydromechanical grease interceptor?
A plumbing appurtenance that intercepts free-floating fats, oils and grease, with continuous separation by air entrainment, buoyancy and interior baffling (IPC/UPC definition). They are rated by flow in gallons per minute and sized with methods like PDI-G101.
What is a gravity grease interceptor?
Under the 2021 IPC and UPC definitions, a gravity grease interceptor has a capacity of at least 500 gallons and separates grease by gravity during a retention time of at least 30 minutes. Some local codes differ (New York City's code uses 300 gallons).
Which one does my restaurant need?
Your city decides. Many require a gravity interceptor for new restaurants or anything with a dishwasher (Austin requires at least 500 gallons with a dishwasher; Knoxville requires a gravity interceptor with automated dishwashing). Others accept hydromechanical units for low-grease businesses.
More guides
Sources
- ICC, 2021 IPC and UPC Essentials (definitions, IPC 1003.3.2 and 1003.3.3)
- New York City Plumbing Code definition of grease interceptor (UpCodes)
- City of Tampa, Grease Trap Definitions
- Austin Water, Grease Trap Sizing & Design Criteria
- JEA, FOG Program Small Trap Maintenance Requirements
- Seattle Public Utilities, FOG: Commercial Kitchens
- City rules quoted on this page come from each linked city page, which lists its official sources and the date checked.