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 a 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:

• If grease layer is over 12 inches AND sludge layer is over 6 inches: pump
• If grease alone is over 18 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

With the tank empty:

• 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

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 (fines $500 to $5,000 per violation)
• 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.