What Your Grease Trap Actually Does
Every commercial kitchen produces FOG -- fats, oils, and grease -- as a byproduct of cooking and dish washing. FOG is the primary cause of sanitary sewer blockages in municipalities nationwide. To prevent that FOG from entering the public sewer system, health codes require food service establishments to install and maintain grease interceptor devices before their drain lines connect to the municipal sewer.
A grease trap works through a straightforward physical process: wastewater from the kitchen flows into a sealed tank, where it slows and cools. FOG, which is lighter than water, floats to the top and is retained in the trap. Heavier food solids sink to the bottom as sludge. The clarified water in the middle exits into the sewer line. Over time, the floating FOG layer and the bottom sludge layer both grow until the trap can no longer function, at which point untreated grease passes directly into the sewer.
Types of Grease Interceptor Systems
Passive hydromechanical grease interceptors (HGIs) are the most common type in smaller food service operations. Typically installed under the sink or in a nearby floor vault, these units hold 20 to 100 gallons and must be serviced frequently, sometimes weekly, because their small capacity fills quickly. They work well for low-volume operations like delis, coffee shops, and small cafes.
Automatic grease removal units (AGRUs) use a heating element and mechanical skimmer to remove collected grease on a timed cycle, depositing it into a separate collection container. These units self-service more continuously than passive traps, but still require regular inspection and waste removal from the collection canister.
Large capacity grease interceptors (LCGIs), also called gravity interceptors or outdoor grease traps, are buried concrete or fiberglass tanks installed in the ground outside the building. These hold 500 to 2,000 gallons or more and are required for high-volume operations like hotel kitchens, cafeterias, and large restaurants. They need pumping every 1 to 3 months depending on volume.
The 25% rule: Most health jurisdictions require servicing when the combined FOG and sludge layers reach 25% of the total tank capacity. Waiting until the trap is full is already a violation. Our technicians measure and record fill levels on every visit.
Cleaning Frequency and Regulatory Requirements
The EPA's Clean Water Act and most municipal sewer-use ordinances require food service establishments to maintain grease traps in proper working order. In practice, this means:
- Written service schedules and records available for inspection
- Licensed waste haulers for grease disposal (not drain disposal)
- Grease waste manifests documenting pickup, transport, and disposal
- No chemical additives that merely liquefy and pass FOG into the sewer
Cleaning frequency depends on kitchen volume and trap size. A quick-service restaurant may need monthly service. A full-service restaurant with a 1,000-gallon interceptor may be on a quarterly schedule. Dr Plumber LLC will assess your operation and recommend a schedule that keeps you in compliance without over-servicing.
The Pumping and Cleaning Process
Professional grease trap service is not simply vacuuming out the contents. A thorough cleaning involves removing all accumulated FOG and sludge, inspecting and cleaning the baffles and inlet and outlet pipes, scraping the tank walls and lid, and verifying that all components are intact and properly seated. Baffles that are cracked or missing allow grease to pass directly through the trap -- a common finding in neglected systems.
After pumping, our technician completes the grease waste manifest documenting the volume removed, the disposal facility used, and the condition of the trap. You receive a copy for your records. If repairs are needed -- cracked baffles, broken lids, damaged inlet pipes -- we identify them during the service visit and provide an estimate before performing any additional work.
Grease-to-Energy Programs
Collected brown grease (the trap waste) can be processed into biodiesel and renewable energy rather than going to a landfill. Many municipalities and waste processors now accept restaurant grease waste for conversion. Dr Plumber LLC partners with licensed disposal facilities that participate in these programs, so your grease waste is handled responsibly and your manifest reflects an environmentally sound chain of custody.
Signs Your Grease Trap Needs Immediate Service
- Slow drains in the kitchen (first sign of a full or partially blocked trap)
- Sewage or rotten egg odors in or around the kitchen
- Grease visible in floor drains or backing up into sinks
- Failed inspection or notice of violation from the health department
- The trap has not been serviced in more than 90 days
Do not wait for a failed inspection to schedule service. Fines for grease trap non-compliance in most jurisdictions start at several hundred dollars per violation and can escalate to permit suspension or forced closure. The cost of regular service is a fraction of a single inspection penalty.