Quick Answer

Grease trap cleaning includes pumping accumulated FOG and solids, high-pressure flushing of inlet and outlet lines, baffle inspection and cleaning, and an inspection certificate for Michigan food service compliance. Under-sink interceptors: $200–$500. In-ground traps: $400–$1,200. Michigan’s 25% rule requires service before accumulation reaches 25% of trap capacity — typically quarterly for high-volume kitchens, biannual for lower-volume operations. Part of Bison’s Hydro Jetting and Commercial Plumbing services.

⚠ Michigan Food Service Compliance Requirement

The 25% Rule — Michigan’s Grease Trap Maintenance Standard

Michigan food service regulations require that grease interceptors be maintained so that accumulated grease and solids do not exceed 25% of the trap’s liquid capacity. When accumulation exceeds this threshold, the trap is no longer effectively intercepting FOG — grease bypasses the interceptor and enters the municipal sewer system.

Health department inspectors check grease trap maintenance records during routine food service inspections. A trap without a current service record, or one showing evidence of FOG bypass in the drain lines, constitutes a violation. A documented maintenance schedule — with inspection certificates on file — is the compliance evidence required.

25%Michigan maximum FOG accumulation before service is required — the 25% rule
QuarterlyRecommended service frequency for high-volume restaurant kitchens
📄Inspection certificate provided after every service — your compliance documentation
2 TypesUnder-sink interceptors and in-ground traps — both serviced by Bison

What a Full Grease Trap Cleaning Includes

Bison’s Grease Trap Cleaning Process — 5 Steps

1

Access & Assessment

Trap lid removed and interior level assessed. FOG and solids depth measured against trap capacity — documents the accumulation percentage for the service record.

2

Full Pumping

All accumulated FOG and solid waste pumped from the trap. Waste transported for compliant disposal. The trap is pumped to full empty — not just the surface layer.

3

Inlet & Outlet Line Flush

High-pressure water flush of both the inlet line (from the kitchen to the trap) and the outlet line (from the trap to the municipal sewer). Removes grease deposited in the connecting lines that bypasses the trap body.

4

Baffle Inspection & Clean

Trap baffles — the internal barriers that separate FOG from the effluent — are inspected for damage and cleared of any accumulated grease. Damaged baffles are documented for repair or replacement.

5

Inspection Certificate

Service date, trap size, waste volume removed, and technician signature documented on the inspection certificate. This is the compliance record your health inspector requires.

Two Types of Grease Interceptors — Service Comparison

Small to Medium Volume

Under-Sink Grease Interceptor

$200–$500 per service
CapacityTypically 20–70 gallons — small interceptor installed under or near the sink
LocationInside the kitchen — under the prep sink, dishwasher drain, or in a floor box
Typical forCafes, bakeries, small quick-service, food trucks with fixed locations, office cafeterias
Service freq.Monthly to quarterly — smaller capacity fills faster under regular cooking load
IndicatorSlow sink drainage, grease odor from the floor drain, visible FOG at the sink drain
High Volume Commercial

In-Ground Grease Trap

$400–$1,200 per service
Capacity500–2,000+ gallons — large concrete or fiberglass tank installed below grade
LocationOutside the kitchen — buried in the parking area or adjacent yard, accessed by a lid
Typical forFull-service restaurants, hotel kitchens, school cafeterias, high-volume catering facilities
Service freq.Quarterly to biannual depending on daily FOG output and tank capacity
IndicatorKitchen drain backups, grease odor outside the building, slow flow in floor drains

What Happens When a Grease Trap Isn’t Maintained

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Kitchen Drain Backups

When the trap is at capacity and FOG bypasses it, grease accumulates in the kitchen drain lines downstream of the interceptor. The result is progressive drain restriction and eventual backup — typically during peak service when kitchen drain load is highest. A backup during lunch or dinner service is an operational emergency.

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Health Code Violation

Michigan food service health inspectors check grease trap maintenance records. A trap without current service documentation, a trap exceeding the 25% accumulation threshold, or FOG evidence in the drain lines constitutes a violation that can trigger a closure order until the condition is corrected and re-inspected.

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Municipal FOG Surcharge

When FOG from a commercial kitchen reaches the municipal sewer main — because the grease trap failed to intercept it — Macomb County and Oakland County water authorities can assess FOG discharge surcharge fees against the property. These fees are assessed per violation and are separate from the cost of corrective drain cleaning.

Service Scheduling — How Often Does Your Trap Need Cleaning

Recommended Grease Trap Service Frequency by Kitchen Type

The right service interval is determined by trap size relative to daily FOG output. Bison assesses the appropriate schedule during the initial service visit based on trap capacity and kitchen volume.

Monthly–Quarterly
Under-Sink Interceptors

Small-capacity interceptors under 70 gallons fill quickly under regular cooking loads. Monthly service for active kitchens, quarterly for lighter use.

Quarterly
High-Volume Restaurants

Full-service restaurants with in-ground traps, deep fryers, and high daily cover counts. Quarterly service prevents the 25% threshold from being exceeded between visits.

Biannual
Lower-Volume Operations

Cafes, bakeries, office cafeterias, and low-volume food service with in-ground traps. Biannual service is sufficient when daily FOG output is significantly below trap capacity.

What the Inspection Certificate Documents

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Service Date and Next Service Recommendation

The date the trap was serviced, the name of the Bison technician, and the recommended next service date based on the trap size, accumulation level found, and kitchen volume. This recommendation becomes the basis for scheduling the next service visit on a contract or standing appointment.

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Accumulation Percentage at Time of Service

The measured FOG and solids depth at the time of service expressed as a percentage of trap capacity — the key compliance metric under Michigan’s 25% rule. This figure is the primary data point a health inspector reviews when assessing whether the trap maintenance schedule is adequate for the kitchen’s operating volume.

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Waste Volume Removed

Total volume of FOG and solid waste pumped from the trap, documented in gallons. This figure provides the historical record needed to identify trends in accumulation rate — useful for adjusting service frequency when kitchen volume increases or when a trap is undersized for the operation’s FOG output.

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Baffle and Trap Body Condition Notes

Any damaged, missing, or deteriorated baffles noted on the certificate. Baffle damage is a maintenance finding that requires follow-up — a damaged baffle allows FOG to bypass the separation zone and reach the outlet line, defeating the trap’s function even when the tank is not at capacity. The inspection certificate documents the condition so repair can be scheduled.

ServiceCost RangeNotes
Under-Sink Interceptor Cleaning$200–$500Pumping, inlet/outlet line flush, baffle inspection, inspection certificate. Typical for cafes and lower-volume food service.
In-Ground Grease Trap Cleaning$400–$1,200Lid removal, full pumping, line flushing, baffle inspection, inspection certificate. Range depends on trap size and waste volume.
Service Contract — QuarterlyReduced per-visit rateQuarterly scheduled cleaning for high-volume kitchens. Reduced per-visit pricing vs. one-off calls. Contact Bison for quote.
Service Contract — BiannualReduced per-visit rateBiannual scheduled cleaning for lower-volume food service and in-ground traps. Reduced per-visit pricing on standing contract.
💡 Grease Trap + Kitchen Drain Jetting — Complete FOG Management

Grease trap cleaning removes the FOG accumulated in the interceptor — but the inlet and outlet lines connecting the kitchen to the trap also accumulate grease buildup that restricts flow over time. Combining grease trap cleaning with commercial kitchen drain hydro jetting in the same service visit provides complete FOG management — a clean trap and clean drain lines — in a single mobilization at a combined rate.