Grease Trap and Interceptor Maintenance

Why this matters

A restaurant's grease trap is the highest-fee commercial septic service in most markets. A typical 1,500 gallon grease interceptor at a restaurant requires pumping every 30 to 90 days at moderate per service. The restaurant owner who skips service produces grease overflow into the municipal sewer (a violation; major fines) or into the septic drainfield (drainfield failure). The local jurisdiction may also have specific FOG (fats, oils, and grease) ordinances requiring documented inspection and pumping records. A commercial septic contractor who can deliver consistent grease-trap service plus the documentation owns a recurring revenue stream that is hard for competitors to displace.

Why grease matters

Fats, oils, and grease (FOG) from food preparation:

• Solidify in cool drain lines (around 80 F or below)
• Coat the inside of pipes
• Combine with other waste (food particles, soap, hair) to form blockages
• Build up over time, eventually closing the pipe
• The classic municipal-sewer blockage that produces sanitary sewer overflow (SSO)

A grease trap or interceptor (the larger commercial version) sits between the kitchen drains and the building's main sanitary line. It traps grease in a tank where it can be pumped out periodically.

Grease trap types

Most modern restaurants use a 1,000 to 3,000 gallon in-ground interceptor with regular pumping.

Pumping schedule

The "25 percent rule" (used by many jurisdictions and most engineering standards):

• Pump when grease layer + sludge reaches 25 percent of total tank volume
• For a 1,500 gallon tank: pump when grease + sludge = 375 gallons

For a typical restaurant:

• Quick-service restaurant: every 30 to 45 days
• Casual dining: every 45 to 90 days
• Fine dining: every 30 to 60 days
• Pizza or burger chain: every 30 to 60 days
• School cafeteria: every 90 to 180 days

Customer-specific service schedule should match actual buildup rates. A 90-day inspection in the first year establishes the right cadence.

Tools and materials

• Vacuum truck (specialized grease-rated truck)
• Long-handled grease measurement tool (sludge judge for grease)
• Hose for cleanup
• Pumping log forms (per jurisdiction requirements)
• Cleanup supplies (degreaser, rags)
• Full PPE (grease is biohazard-rated; same precautions as septic)

Procedure

Step 1: Verify the service schedule

• Confirm with the customer the date of last pumping
• Check the service log
• Verify the trap's location and access

Step 2: Open the trap

• Remove the access lid (typically heavy concrete or steel)
• Use mechanical assistance for heavy lids

Step 3: Inspect contents

Measure with the sludge judge:

• Grease layer thickness (typically 1 to 24 inches)
• Effluent layer thickness
• Sludge layer thickness (settled solids at bottom)

The grease layer is on top (floats), the sludge is on the bottom, effluent in the middle.

For a 1,500 gallon tank that is 5 ft deep with the waterline at 4 ft depth:

• 25 percent of the 48 inch liquid depth is 12 inches, so pump when grease plus sludge combined exceeds 12 inches
• If grease alone exceeds 12 inches (regardless of sludge): pump

Step 4: Pump the trap

The vacuum truck:

1. Inserts hose into the trap
2. Vacuums out grease, effluent, and sludge
3. Continues until tank is essentially empty (residual water OK; significant residual is not)

The pumped content is hauled to a licensed processing facility. Disposal cost is part of the service fee.

Step 5: Inspect after pumping

An in-ground grease interceptor is a permit-required confined space under OSHA 29 CFR 1910.146. It has limited entry and exit, it is not designed for continuous occupancy, and it generates hydrogen sulfide and displaces oxygen. Workers die in these tanks every year, and a high fraction of the fatalities are the second person, who went in after the first one collapsed.

Do this inspection from OUTSIDE the tank. Every item below is doable from grade with a light, a mirror or inspection camera, and a probe:

• Inspect tank walls for cracks or damage
• Inspect baffles and inlet/outlet pipes
• Check the flow path: inlet to outlet should be clear
• Verify the trap is structurally sound

If something genuinely cannot be assessed from grade, that is not a reason to climb in. It is a separate scheduled job under a written permit-space program with atmospheric testing, continuous ventilation, a harness and retrieval line, and an attendant who does not enter under any circumstances. If your shop does not run that program, subcontract the entry. Never enter to retrieve a dropped tool.

Step 6: Restart

• Refill the tank with clean water (typically a hose run from a nearby hose bib)
• Refilling ensures the trap functions immediately (the inlet baffle requires water to operate correctly)

Some jurisdictions allow the trap to refill naturally with the first restaurant operation; verify local practice.

Step 7: Close the tank

• Replace the access lid
• Verify the lid seals properly
• Lock if required

Step 8: Document

Required documentation:

• Service date and technician
• Trap location and ID
• Grease / sludge / effluent measurements
• Quantity pumped
• Disposal facility
• Next service due

Provide copies to:

• Customer (for their compliance file)
• Local jurisdiction (some require copies submitted)
• Contractor's own service records

Step 9: Customer communication

• Confirm next service date
• Identify any maintenance issues observed
• Recommend changes to use pattern if grease accumulation is excessive

Common issues

Excessive grease accumulation

If the trap fills faster than expected:

• Customer's kitchen practices (excess oil, no waste-disposal of fryer oil)
• Trap may be undersized for the operation
• Some staff may be using the trap as a fryer-oil disposal (illegal in most jurisdictions; significant fine)

Educate customer; verify legal disposal of cooking oil.

Trap not functioning (effluent bypass)

If grease is appearing in the downstream sewer despite pumping:

• Inlet or outlet pipe may have shifted (loss of baffling)
• Trap may be inadequately sized for flow
• Customer's drain configuration may bypass the trap

Inspect; correct as needed.

Frozen trap

In cold climates, in-ground traps may freeze if:

• Tank cover is shallow
• No insulation
• Limited use (slow flow doesn't keep warm)

Insulation or heating may be required.

Odor

Strong odor from the trap area:

• Trap may be due for pumping
• Trap may have damaged baffles allowing gas to escape
• Trap vent (if equipped) may be blocked

Local jurisdiction FOG ordinances

Many municipalities have specific FOG ordinances:

• Required pumping intervals (e.g., minimum quarterly)
• Required documentation
• Required disposal facility certification
• Penalty for non-compliance (per-violation fines set by the local sewer-use ordinance, often escalating on repeat findings and sometimes assessed per day; pull the current schedule from the jurisdiction, since these get revised without notice to haulers)
• Inspection access for jurisdiction representative

Verify the customer's jurisdiction's specific requirements. Service contracts should include all required documentation.

Auto grease removal devices (GRD)

Some installations use automated grease removal devices:

• Skim grease from the surface continuously
• Pump to a separate collection container
• Reduce frequency of full trap pump-out

GRDs cost a significant install plus ongoing service. Worth it for high-volume operations.

References

• Local FOG ordinances (vary by jurisdiction).
• EPA Best Practices for Restaurant Wastewater Management.
• Plumbing and Drainage Institute (PDI) standards.
• ASME A112.14 (Grease Interceptors).
• IAPMO/ASME A112.14 (Grease Interceptors and Grease Removal Devices).
• Manuall internal: Septic Septic Inspection, Septic Septic Pumping Service.