Grease Interceptor Maintenance: What Restaurant Owners Need to Know

If you operate a restaurant, food truck commissary, institutional kitchen, or any food service business in Ontario, grease interceptor maintenance is not optional — it is a legal obligation with real consequences for non-compliance. Yet many restaurant owners are uncertain about exactly what their unit is, how it works, how often it needs service, and what happens if something goes wrong.

This guide from Mechora Group's commercial plumbing team walks through everything a food service operator in Ontario's GTA region needs to know: what a grease interceptor does, why it matters to the municipal sewer system, what the regulations require, and how to keep your facility in full compliance.

What Is a Grease Interceptor and How Does It Work?

A grease interceptor — also commonly called a grease trap at smaller scales — is a plumbing device installed in the drainage system of a commercial kitchen. Its sole purpose is to intercept fats, oils, and grease (collectively called FOG) before that wastewater enters the municipal sewer system.

The operating principle is straightforward: gravity separation. Wastewater from kitchen sinks, dishwashers, floor drains, and cooking equipment flows into the interceptor's inlet. Inside the device, the flow slows dramatically, allowing three layers to form. Grease and oils, being less dense than water, float to the top and accumulate as a grease cap. Solid food particles, being denser than water, settle to the bottom as a sludge layer. The relatively clean water in the middle zone — the effluent — exits through the outlet and proceeds to the sanitary sewer.

This basic mechanism has not changed significantly in over a century. What has evolved is the scale, installation method, and monitoring requirements for modern commercial applications.

Grease Trap vs. Grease Interceptor: Understanding the Difference

The terms "grease trap" and "grease interceptor" are often used interchangeably, but they describe two distinct device categories with different applications:

Grease traps are small, hydromechanical devices typically installed under or adjacent to a single sink or a small group of fixtures. They hold anywhere from 20 to 100 litres and are designed for lower-volume operations. They require very frequent cleaning — often weekly or biweekly — because their small capacity fills quickly. In Ontario, under-sink grease traps are generally acceptable only for specific low-volume applications; high-volume commercial kitchens are required to use larger interceptors.

Grease interceptors are large, gravity-based units typically installed outside the building, buried below grade. They may hold 1,000 litres or more. They receive all kitchen wastewater from the building before it reaches the municipal sewer connection. Because of their larger capacity and lower flow velocity, they are far more effective at FOG removal and are the standard requirement for full-service restaurants, cafeterias, and institutional food service operations across Ontario.

Why FOG Is a Problem for the Municipal Sewer System

You might wonder why grease in wastewater warrants such detailed regulation. The answer lies in what happens to FOG once it enters the sewer network.

Fats, oils, and grease do not remain liquid indefinitely. As they cool inside sewer pipes — which are underground and subject to ambient temperatures — they solidify and adhere to pipe walls. Over time, this accumulation constricts the pipe's internal diameter, reducing flow capacity. In worst-case scenarios, the buildup completely blocks the pipe, causing what regulators call a Sanitary Sewer Overflow (SSO) — an uncontrolled release of sewage into the environment, basements, or surface water.

SSOs are expensive to remediate, environmentally damaging, and can create serious public health hazards. They are also becoming more frequent as aging sewer infrastructure meets increasing commercial kitchen output in urban areas. The regulatory framework around grease interceptors exists precisely to prevent individual restaurants from externalizing this cost onto the public sewer system and the municipalities that maintain it.

Beyond the pipes, FOG discharged in excessive quantities can also disrupt the biological treatment processes at wastewater treatment plants, creating further downstream problems.

Ontario Regulatory Requirements for Food Service Establishments

Commercial grease interceptors in Ontario are governed by overlapping layers of regulation. Understanding each layer is essential for compliance:

Ontario Building Code (OBC)

The Ontario Building Code establishes baseline requirements for grease interceptors as part of the plumbing provisions. The OBC requires grease interceptors for food preparation establishments where grease-laden waste is discharged to a drainage system that connects to a public sewer. The OBC specifies sizing methodologies and installation requirements. Any new installation or replacement requires a building permit and inspection.

Municipal Sewer Use Bylaws

Every municipality in the GTA maintains a Sewer Use Bylaw that independently governs what can be discharged to the municipal sewer system. These bylaws typically set maximum allowable concentrations of fats, oils, and grease in discharge, require grease interceptors for qualifying food service operations, mandate regular maintenance and pump-outs, and require documentation and record-keeping.

Municipal bylaws often go beyond what the OBC requires and are enforced independently by municipal bylaw officers or environmental compliance staff who may conduct unannounced inspections.

Toronto Sewer Use Bylaw

For businesses operating in the City of Toronto, the City's sewer use bylaw governs grease interceptor requirements. Business owners should verify the current requirements directly with the City of Toronto's Municipal Licensing and Standards or Toronto Water, as bylaw provisions and specific concentration limits are periodically updated. The bylaw establishes discharge limits, mandates interceptor installation and maintenance, and requires businesses to retain pump-out manifests.

Required Pumping Frequency

The most common question from restaurant operators is: how often does a grease interceptor actually need to be pumped?

Most Ontario municipalities apply a 25% rule: the combined depth of the floating grease cap and the bottom sludge layer must not exceed 25% of the total liquid depth in the interceptor. When that threshold is reached, a pump-out is mandatory regardless of when the last service occurred.

In practice, a busy full-service restaurant with a properly sized interceptor will typically require pump-outs every one to three months. Factors that accelerate fill rate include:

• High-volume fryer operations
• Multiple shifts or extended operating hours
• Inadequate pre-scraping of dishes and cookware before washing
• Undersized interceptor relative to actual kitchen output
• Improper discharge of solid food waste into drains

Your licensed waste hauler is required to measure and record the grease and sludge levels at each pump-out. If they are consistently finding the unit nearly full on each visit, your pumping frequency may need to increase or your interceptor may need upsizing. If it is consistently near empty, you may be able to extend intervals — but only with documentation and, in some municipalities, prior approval.

Manifest Requirements and Documentation

Every grease interceptor pump-out must be performed by a licensed waste hauler registered with your municipality. A pump-out performed by an unlicensed party does not satisfy the bylaw requirement.

For each pump-out, your hauler must provide a manifest — a document recording the date, location, volume removed, hauler's licence number, and disposal destination. You are required to retain these manifests — typically for a minimum of two years — and have them available for municipal inspection on request.

Beyond manifests, maintain your own log that includes:

• Date of each service visit
• Grease and sludge levels recorded before pump-out
• Volume of material removed
• Any noted concerns or repairs
• Hauler company name and licence number

This documentation is your protection in the event of a municipal inspection or dispute. Businesses with clean, consistent maintenance records are treated very differently from those with no records at all.

Signs of a Failing or Full Grease Interceptor

Your grease interceptor will give you warning signs before it causes a major problem. Watch for:

• Slow kitchen drains — especially across multiple fixtures simultaneously, indicating the interceptor's outlet is restricted
• Drain backup or overflow — the most serious sign; cease operations and call a plumber immediately
• Persistent foul odour — rotten or sulphurous smell near floor drains or the interceptor access point
• Gurgling sounds from drains — indicates restricted flow or partial blockage
• Water pooling near the interceptor or on the kitchen floor
• Pest activity near the interceptor, which can indicate accumulated organic material

If you notice any of these signs, contact a licensed commercial plumber immediately. Waiting will only make the problem worse and more expensive to remediate.

Proper Pumping Procedure

A proper grease interceptor pump-out is more than simply vacuuming out the contents. A compliant pump-out includes:

1. Full pump-out of all liquid and accumulated material — the unit should be emptied completely, not just partially drawn down
2. Lid and baffle inspection — the hauler should inspect inlet and outlet baffles for damage, cracks, or missing components
3. Interior inspection — checking for structural issues, cracks, or corrosion in concrete or fibreglass units
4. Flush and rinse — the interior walls should be rinsed with clean water to remove adhered grease
5. Measurement recording — grease and sludge depths should be measured and recorded before pump-out
6. Manifesting — a proper waste manifest completed and provided to the operator

The pumped waste is classified as non-hazardous liquid industrial waste and must be transported to an approved disposal or treatment facility. Your hauler is responsible for compliant disposal, but you should confirm their facility is properly licensed.

Prohibited Disposal Methods: Biological Treatments

The market is full of biological enzyme products, bacteria additives, and "bioremediation" treatments marketed to restaurant operators as a way to maintain grease interceptors between pump-outs or reduce pump-out frequency. Ontario business owners should understand the limitations and regulatory status of these products.

Biological additives are not an acceptable substitute for mandatory mechanical pump-outs. Most Ontario municipal sewer use bylaws explicitly prohibit relying on biological treatments as a compliance strategy. The reason is straightforward: while these products may partially break down grease inside the interceptor, they effectively transfer that grease into the sewer system in liquid form — which is exactly what the interceptor is designed to prevent. Broken-down fats can re-solidify further downstream, potentially causing blockages at someone else's connection or deeper in the sewer network.

Some municipalities permit biological additives as a supplement between scheduled pump-outs, provided pump-outs still occur at the required intervals. Check your local bylaw before using any such product, and never use them as a justification for extending pump-out intervals beyond what is permitted.

Sizing Requirements for Commercial Kitchens

A grease interceptor must be correctly sized for the volume of wastewater it will receive. An undersized unit fills quickly, requires more frequent pump-outs, and is more likely to pass FOG to the sewer system. An oversized unit creates its own problems — extended retention can cause the interceptor to become septic, generating hydrogen sulphide gas and creating odour issues.

Ontario Building Code sizing methodologies consider:

• The number and type of fixtures discharging to the interceptor
• Peak flow rate from connected fixtures
• Required grease retention time (typically 30 minutes minimum)
• Anticipated operating hours and volume

For new construction or commercial kitchen renovations, sizing calculations are performed by a licensed plumber as part of the permit application. If your kitchen's output has increased significantly since your interceptor was installed — through expanded hours, additional equipment, or higher seat count — the original sizing may no longer be adequate and a reassessment is warranted.

New Construction Requirements

If you are opening a new restaurant or renovating an existing commercial space in Ontario, the grease interceptor must be designed and installed as part of the permitted plumbing work. This means:

• Engaging a licensed plumber to design the grease control system before construction begins
• Obtaining a building permit for the plumbing work, which includes grease interceptor installation
• Municipal inspection of the installation before backfilling or covering
• Final inspection and approval before occupancy

Retroactive installation — fitting an interceptor after a kitchen is operating without one — is significantly more expensive than planning for it during construction. Mechora Group's construction plumbing team regularly works with restaurant developers and operators on grease management systems for new builds and major renovations.

Inspections and Non-Compliance Consequences

Municipal environmental compliance staff and bylaw enforcement officers have the authority to inspect commercial premises for grease interceptor compliance. Inspections may be triggered by complaints from neighbours, reports of sewer issues in your area, or routine compliance checks in your commercial zone.

An inspector will typically want to see your maintenance log and manifests, verify the unit is accessible and functioning, check discharge for FOG levels, and confirm your interceptor is properly sized and permitted.

Consequences for non-compliance in Ontario can include:

• Written orders requiring immediate corrective action
• Fines under the municipal sewer use bylaw
• Orders to cease discharge to the sewer until compliance is achieved
• Charges under the Ontario Water Resources Act in serious cases
• Cost recovery orders requiring the business to pay for sewer remediation caused by their discharge

The potential cost of non-compliance far exceeds the cost of a regular maintenance program. Mechora Group's commercial plumbing services can help you establish a compliant maintenance schedule and resolve any outstanding issues before they escalate.

Mechora Group Commercial Plumbing Services

Mechora Group Inc. is a Licensed & Insured commercial and residential plumbing contractor serving the Greater Toronto Area including Toronto, Mississauga, Brampton, Vaughan, Markham, and Oakville.

Our commercial plumbing services for food service operators include grease interceptor sizing and installation, building permit assistance, inspection of existing interceptors, baffle and component repair, system relocation or upsizing for expanded kitchens, and drainage system assessment for new restaurant build-outs.

We work directly with restaurant operators, property managers, and developers throughout the permitting and construction process to ensure your grease management system meets all applicable code and bylaw requirements from day one.