"How often?" is the first question most operators have about grease trap maintenance. The honest answer is: it depends on your kitchen. A fast-food fryer operation running three shifts has a very different FOG output than a catering company that uses the kitchen twice a week. This article gives you the framework to figure out your specific interval — and how to adjust it if conditions change.
The Threshold Rule: 25% Capacity
Before discussing any calendar-based interval, understand the underlying principle: the correct time to clean a grease trap is when it reaches 25% capacity — when the combined depth of floating FOG and settled solids equals one-quarter of the trap's total liquid depth.
Beyond this threshold, the effective separation zone shrinks too much for reliable FOG capture. Grease begins passing through the trap and entering the sewer lateral. From a compliance standpoint, a trap above 25% at the time of an inspection is typically an automatic violation regardless of when it was last serviced.
This means the right cleaning interval is the one that keeps you consistently below 25% — not a fixed calendar date you apply to every kitchen. Your actual interval depends on how quickly your specific trap fills, which depends on several variables.
Factors That Determine Your Cleaning Interval
Kitchen Type and Menu
The biggest variable. A fried chicken restaurant with multiple large fryers generates far more FOG per cover than a deli or bakery. High-grease menus — fried foods, heavy proteins, butter-intensive cooking — fill interceptors faster. Light-fare kitchens stretch intervals further. A coffee shop may run quarterly; a burger joint may need biweekly service.
Trap Size
A 1,500-gallon outdoor gravity interceptor reaches 25% at 375 gallons accumulated FOG and solids. A 50-gallon under-sink unit reaches 25% at just 12.5 gallons. The under-sink trap fills much faster in absolute terms. Trap size determines not just frequency but also the practical logistics of service.
Daily Cover Count and Operating Hours
More covers means more dishwashing, more food preparation waste, and more water through the trap. A restaurant doing 400 covers per day accumulates FOG roughly four times faster than one doing 100 covers. Extended operating hours and high-volume event periods (holidays, catering events) accelerate fill rates temporarily.
Staff Practices
Kitchens where staff consistently dry-wipe cookware, dispose of cooking oil through proper channels, and avoid the garbage disposal reduce their FOG load and extend service intervals. Kitchens where these practices are inconsistent fill traps faster than the equipment alone would predict.
General Frequency Ranges by Operation Type
These are widely-cited industry guidelines — useful starting points, but not substitutes for monitoring your actual fill rate. Local ordinance minimums always apply; many jurisdictions set mandatory floors regardless of fill level.
| Kitchen Type | FOG Output | Under-Sink HGI Interval | Large Outdoor GGI Interval |
|---|---|---|---|
| High-volume fried food (multiple fryers, high covers) | Very High | Weekly – biweekly | Monthly |
| Full-service restaurant (standard menu) | High | Every 4–6 weeks | Quarterly |
| Moderate-volume (café, deli, light cooking) | Medium | Monthly – every 8 weeks | Quarterly – semi-annual |
| Low-volume / low-FOG (coffee shop, minimal food prep) | Low | Quarterly | Semi-annual or variance eligible |
Always check your local ordinance for the required minimum frequency. You may be able to extend beyond the minimum if your fill rate supports it, but you cannot legally go below the minimum even if the trap is not at 25%.
How to Establish and Calibrate Your Schedule
If you're new to a location: ask for the previous operator's service records or consult your hauler for their assessment of the trap's fill rate based on your kitchen's volume. If you're starting fresh, set an initial interval based on your kitchen type, then monitor fill levels at scheduled visits and adjust accordingly.
After each service visit, ask your contractor to note the fill level percentage in the service report or manifest. Tracking this number over time tells you whether your interval is correct — and gives you data to justify an extension or flag the need for more frequent service.
The right approach: after each professional service visit, ask your hauler what percentage capacity the trap was at when they arrived. If it was consistently at 10-15%, you may be able to extend the interval. If it was consistently at 22-25% or above, shorten the interval. A hauler who's been servicing your trap for multiple visits should be able to tell you the trend.
Build seasonal adjustments into your schedule. If your operation runs significantly higher volume during summer, holiday periods, or local event seasons, consider adding a service visit during those periods even if your standard interval doesn't require it.
Regulatory Minimums vs. Operational Reality
Some operators misread "quarterly minimum" in their local ordinance as the recommended frequency. It's the floor, not the recommendation. A quarterly requirement means you must have the trap serviced at least once every 90 days — it doesn't mean quarterly is adequate for a high-volume kitchen with a small interceptor.
Treating the quarterly minimum as the recommended frequency is one of the most common compliance mistakes in high-volume kitchens. A quarterly requirement means you must be serviced at least once every 90 days — it does not mean quarterly is adequate for your operation if your trap reaches 25% more frequently.
Operating a high-FOG kitchen on a quarterly schedule when your trap actually hits 25% monthly means you're out of compliance for two months of every three. The inspection risk and the operational risk (slow drains, odors, potential backup) are both real. Schedule to your actual fill rate, not to the regulatory minimum.
For a full overview of compliance requirements including minimum frequency obligations, see the FOG compliance guide. For a complete maintenance program, see the grease trap maintenance guide.
Warning Signs That Your Current Schedule Is Insufficient
Between scheduled visits, these signs indicate you're filling faster than your interval assumes and need to move up your next service:
- Drains that are notably slower than normal
- Sulfur or sewage odors from kitchen drains during service hours
- Greasy water backing into sink basins
- Any sewage backup through floor drains — this requires emergency service, not a rescheduled visit
For the full list of indicators and how to respond, see signs your grease trap is full.
Frequently Asked Questions
How often does a restaurant grease trap need to be cleaned?
It depends on trap size and kitchen volume. High-volume kitchens with small under-sink interceptors may need service weekly or biweekly. Large outdoor gravity interceptors for moderate-volume restaurants are typically serviced quarterly. The universal threshold is 25% capacity — when FOG and solids reach that level, the trap should be serviced regardless of when it was last cleaned. Check your local ordinance for mandatory minimum frequencies.
What happens if you don't clean a grease trap often enough?
FOG exceeds the 25% threshold and begins bypassing the trap into the sewer lateral. Downstream effects: blockages in your drain line, slow drains, sewage odors, eventual backups. Compliance effects: a trap found above 25% during an inspection is typically a violation. Emergency service costs substantially more than scheduled service. Repeated violations can result in escalating fines or permit action.
Can I extend my grease trap cleaning schedule to save money?
Only if your actual fill rate supports it and your local ordinance permits it. If your trap is consistently well below 25% at service time, discuss the data with your hauler and check whether your jurisdiction allows extended intervals. Do not extend the interval below your local ordinance's minimum, and do not extend based on assumption — only on actual fill rate data from service visits. The cost of an emergency or a fine from operating above 25% exceeds any savings from extending an interval that's already appropriate.
How do I find out my local grease trap cleaning requirements?
Contact your local wastewater authority or public works department — the same agency that issues grease interceptor permits. They can tell you your jurisdiction's minimum cleaning frequency, documentation requirements, and any specific rules that apply to your operation type or trap size. Your licensed grease trap contractor should also be familiar with local requirements in your service area.
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Author: Grease Trap Locator Editorial Team
The Grease Trap Locator editorial team covers FOG compliance, grease trap maintenance, and commercial kitchen regulations across the US and Canada. Our guides are written for restaurant owners, facility managers, and food service operators who need practical, accurate information without the fluff.
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