Grease interceptor rules require any commercial kitchen or similar facility to install a properly sized, certified unit; pump it before accumulated grease and solids reach 25% of the tank’s liquid depth; keep cleaning records available for inspection; avoid hot-water flushes and chemical additives that push grease downstream; and follow OSHA confined-space procedures during maintenance. The framework comes from federal pretreatment standards under the Clean Water Act, the International Plumbing Code, and local sewer ordinances that put teeth behind both.1eCFR. 40 CFR 403.5 – National Pretreatment Standards: Prohibited Discharges
Which Businesses Are Covered
The International Plumbing Code requires a grease interceptor for any facility producing grease-laden waste from food preparation, which includes restaurants, hotel kitchens, hospitals, school kitchens, bars, factory cafeterias, and clubs.2International Code Council. 2021 International Plumbing Code – 1003.3.1 Grease Interceptors The specific fixtures that trigger the requirement include pot sinks, pre-rinse sinks, wok stations, floor drains where kettles are emptied, and dishwashers without pre-rinse sinks. If a fixture lets fats, oils, or grease reach the drain, it needs to route through an interceptor.
Interceptors for other pollutants follow the same principle but sit outside grease rules: oil-water separators for auto shops and elevator pits, and sand and grit interceptors for car washes. Your local wastewater authority decides which type applies based on what you actually discharge.
Sizing and Certification Before Install
You don’t get to pick the size. Most jurisdictions follow the IPC or the Uniform Plumbing Code, both of which size interceptors using Drainage Fixture Units, a numerical load value assigned to each connected fixture. A three-compartment sink carries a higher fixture unit value than a mop sink or single floor drain, and the total count sets the minimum capacity.
For hydromechanical units, the number translates into a required flow rate in gallons per minute. For gravity units, it translates into a minimum tank volume. Eight fixture units might call for a 20 gallons-per-minute hydromechanical unit or a 500-gallon gravity tank; 35 fixture units can push you to a 1,000-gallon gravity interceptor. Kitchens that include a food waste disposer or pulper generally jump to the next larger gravity size beyond what the fixture calculation alone would produce.
Certification matters as much as size. Hydromechanical interceptors are tested under ASME A112.14.3, which requires at least 90 percent grease removal efficiency at the unit’s rated flow. Your building department reviews the sizing math and the unit’s certification before issuing a permit.
The 25% Rule and Pumping Schedule
The core operating rule is the 25% standard: once the combined depth of floating grease and settled solids reaches one-quarter of the interceptor’s total liquid depth, the unit must be pumped. Past that point the device can no longer separate effectively, and untreated waste starts passing through to the sewer. Most local sewer ordinances have adopted this threshold, though enforcement specifics vary.
Many jurisdictions layer a maximum interval on top of the 25% trigger. A 90-day cycle is common for gravity interceptors, meaning the tank gets pumped at least every three months even if it hasn’t visibly hit the limit. Grease decomposes over time and generates hydrogen sulfide, which corrodes concrete and metal, so regular pumping protects the interceptor itself. Hydromechanical units in high-volume kitchens often need weekly or biweekly service because their capacity is smaller.
A licensed waste hauler performs the pump-out and removes all liquids and solids to restore full capacity. You generally cannot clean a gravity interceptor yourself, because the waste must be transported to an approved disposal facility and haulers need permits for that. Expect service costs from a few hundred to roughly a thousand dollars, depending on tank size and location.
What You Cannot Do
Flushing an interceptor with hot water is prohibited in most jurisdictions. Hot water melts grease just long enough for it to leave the trap, and it re-solidifies inside the sewer main, creating the exact blockage the interceptor was supposed to prevent.
The same reasoning bars enzyme treatments, bacterial additives, chemical solvents, and emulsifiers marketed as grease management products. They liquefy grease temporarily so it passes through the interceptor and congeals downstream. Most municipal sewer ordinances explicitly ban them. Beyond the downstream damage, these additives interfere with the biological processes inside the tank, degrade baffles and gaskets, and can create chemical hazards for workers.
If a vendor claims their product eliminates the need for pumping, treat that as a warning. No additive substitutes for physically removing accumulated grease, and using one can convert a routine inspection into a violation.
Records You Have to Keep
Compliance lives or dies on paperwork. Most local wastewater programs require a cleaning log with the date of each service, the volume of waste removed, and the name of the hauler. Pumping manifests from the hauler prove the waste reached an approved disposal site. Records typically stay on-site, must be available for immediate inspection, and are usually retained for at least two to three years.
FOG inspections are usually unannounced, and the first thing the inspector asks to see is the maintenance log. Missing or incomplete records count as a violation even when the interceptor itself is currently clean, because the records are what prove ongoing compliance between visits. File every manifest and keep them organized.
Automated monitoring systems for larger gravity units use sensors to track grease and liquid levels in real time and send alerts as accumulation approaches 25%. Their data logs supplement paper records and help tune your pumping schedule, but they don’t replace the hauler manifest.
Safety Rules During Cleaning
Gravity interceptors large enough for a person to enter are permit-required confined spaces under OSHA regulations.3Occupational Safety and Health Administration. Grease Trap Hazards Decomposing grease generates methane, hydrogen sulfide, carbon monoxide, and carbon dioxide. Hydrogen sulfide deadens the sense of smell at high concentrations, which removes the very warning signal people rely on to detect it.
Before anyone enters, the atmosphere inside must be tested for oxygen, flammable gases, and toxic gases, in that order.4eCFR. 29 CFR 1910.146 – Permit-Required Confined Spaces Employers must maintain a written confined space program, post danger signs, prevent unauthorized entry, and arrange rescue services capable of responding in time. Workers inside need an exit route such as a ladder, and lockout/tagout procedures apply to any energy sources tied to the interceptor.
Covers over interceptor openings must support at least twice the maximum load that could be placed on them and must be secured against accidental displacement.3Occupational Safety and Health Administration. Grease Trap Hazards Workers who fall into a grease trap can drown, and OSHA has documented fatalities in that exact scenario.
Penalties for Noncompliance
The federal framework starts with the Clean Water Act, which directs EPA to establish pretreatment standards for pollutants entering publicly owned treatment works.5Office of the Law Revision Counsel. 33 USC 1317 – Toxic and Pretreatment Effluent Standards The National Pretreatment Program at 40 CFR Part 403 requires every local sewer authority to run an enforcement program with real authority: inspect any premises with a discharge source, require compliance with pretreatment standards, and seek civil or criminal penalties of at least $1,000 per day per violation.6eCFR. 40 CFR 403.8 – Pretreatment Program Requirements
Enforcement typically opens with an inspection and a Notice of Violation identifying the problem with a deadline to fix it. Common triggers are an interceptor over the 25% limit, missing maintenance records, or evidence of prohibited additives. Correct the issue in time and most cases close. Miss the deadline and fines start running.
The ceiling is higher than most owners expect. Civil penalties under the Clean Water Act can reach $25,000 per day per violation. Administrative penalties come in two tiers: Class I caps at $10,000 per violation with a $25,000 overall maximum; Class II can reach $10,000 per day up to $125,000 total.7Office of the Law Revision Counsel. 33 USC 1319 – Enforcement Criminal prosecution is reserved for the worst cases. Negligent violations carry fines of $2,500 to $25,000 per day and up to one year in jail; knowing violations double those ranges. If a knowing violation places someone in danger of death or serious injury, fines can reach $250,000 for individuals or $1,000,000 for organizations.
Local sewer authorities can also cut off water service or revoke an operating permit for persistent noncompliance. If a blockage caused by your grease discharge triggers a sanitary sewer overflow, you may be liable for cleanup costs on top of regulatory penalties. A single restaurant that ignores its interceptor for six months can create the kind of blockage that backs raw sewage into neighboring businesses or into the street.