A grease interceptor slows kitchen wastewater so fats, oils and grease float and food solids settle before water leaves for the sewer. It must be cleaned before trapped grease and solids fill too much of its capacity; many municipal programs use a 25 percent rule. Kitchen lines upstream and the building sewer downstream also need periodic jetting. Confirm requirements with your municipality.
- An interceptor only works when it has room to hold grease; a full one passes grease straight to the sewer.
- Clean on a schedule based on measured grease and solids, not on a fixed calendar alone.
- Kitchen lines between fixtures and the interceptor still need periodic jetting.
- Keep a service log with dates, volumes removed and hauler records; many municipalities ask for it.
- Municipal sewer use bylaws, not this guide, set the legal requirements for your kitchen.
01 /How does a grease interceptor work?
A grease interceptor, called a grease trap when it is small and under the sink, is a tank that sits between kitchen fixtures and the building sewer. Wastewater enters, slows down, and cools. Grease and oil, being lighter than water, float to the top. Heavier food solids sink to the bottom. The clearer water in the middle leaves through an outlet baffle or pipe set below the grease layer.
The interceptor works only while there is space for grease and solids to collect without reaching the outlet. As the grease layer thickens and solids build up, the effective volume shrinks, water passes through faster, and grease begins to escape into the building sewer and the municipal system.
| Type | Where it sits | Typical service |
|---|---|---|
| Passive under-sink trap | Beneath or beside a sink | Frequent manual cleaning by staff or a service company |
| Automatic or mechanical unit | Near fixtures | Skims grease into a container; staff empty and clean regularly |
| In-ground gravity interceptor | Outside or under the floor, larger tank | Pumped by a licensed waste hauler |
In Canada, grease interceptors are generally designed and rated to CSA standards, and their required sizing and installation are governed by the plumbing code in force and municipal bylaws. Confirm the requirements for your kitchen with your municipality and a qualified plumber.
02 /How often should a grease interceptor be cleaned?
Clean an interceptor before grease and settled solids take up too much of its liquid depth. Many municipal FOG programs in North America use a 25 percent rule: service the interceptor when combined floating grease and settled solids reach 25 percent of the total liquid depth. Some municipalities set a fixed minimum frequency as well. Check what yours requires.
In practice, busy kitchens with small under-sink traps may need cleaning daily or weekly, while larger in-ground interceptors are often pumped monthly to quarterly. Measure, then set the schedule.
- Measure
Use a sludge judge or measuring stick to find the depth of the grease layer and the solids layer, and the total liquid depth.
- Calculate
Add the grease and solids depths and divide by the total liquid depth. At or above 25 percent, or your municipality's threshold, schedule service.
- Record
Log the date, measurements and who took them.
- Adjust
If you reach the threshold before the scheduled service, shorten the interval. If you consistently measure well below, discuss a longer interval with your service provider and confirm it meets bylaw minimums.
03 /What does a complete interceptor service include?
A proper service removes everything, not just the floating grease. Skimming off the top layer and leaving settled solids is sometimes called a “skim” and can leave the interceptor well short of capacity.
- Full pump-out of grease, water and settled solids.
- Scraping of walls, baffles and lids.
- Inspection of inlet and outlet baffles, tees and piping for damage or blockage.
- Check of lid gaskets and seals for odour control.
- Refilling with clean water where the manufacturer recommends it, so the unit works correctly from the start.
- A service record showing date, volume removed, condition observations and the hauler's manifest or disposal record.
04 /Why do kitchen lines need jetting too?
Grease starts cooling the moment it leaves a fixture, so the lines between sinks, floor drains and the interceptor collect grease before it ever reaches the tank. Downstream, any grease that escapes a full or undersized interceptor coats the building sewer. Both sections need periodic cleaning.
Hydro jetting is the standard method for kitchen lines, because it clears grease from the full pipe wall. A cable can open a blocked line in an emergency but tends to leave grease behind, so blockages return. Many kitchens schedule line jetting every three to twelve months depending on volume, menu and the interceptor's performance. Sister site SewerJetting.ca covers jetting equipment and nozzle choice in depth.
Schedule jetting outside service hours and coordinate with the interceptor pump-out, so grease flushed from upstream lines is captured and removed rather than passed on to the sewer.
05 /What kitchen practices reduce grease in the system?
Best management practices in the kitchen reduce how often the interceptor and lines need service, and reduce the risk of violating local discharge limits.
- Dry-wipe pots, pans and plates into organics or garbage before washing.
- Collect fryer oil and bulk grease in a dedicated rendering or recycling container, never down a drain.
- Use strainers in sinks and floor drains, and empty them into organics.
- Do not pour hot water or chemicals down drains to move grease; it simply sets further downstream.
- Avoid emulsifiers and enzyme products that claim to dissolve grease unless your municipality allows them; many programs discourage products that push grease past the interceptor.
- Train staff at onboarding and post short reminders near sinks.
- Keep a shared log of interceptor measurements and services.
06 /What do municipal bylaws usually require?
Most Canadian municipalities regulate what businesses can discharge to the sanitary sewer through a sewer use or wastewater bylaw. For food service businesses, bylaws commonly require an approved grease interceptor, set maintenance expectations, require records to be kept for a period of time, and allow inspections. Specific requirements differ city to city.
In Calgary, the City's wastewater and drainage rules apply; call 311 or check calgary.ca for current requirements for food service premises. Elsewhere, contact your municipality's wastewater or environmental services department.
07 /How should a restaurant choose a grease service provider?
Choose a provider that pumps completely, documents every visit, and can also jet lines and run a camera when needed. Use the same principles as for any sewer cleaner: insurance, workers' compensation coverage, written scope, and clear pricing. See how to hire a sewer cleaner. In-ground interceptors are pumped with vacuum trucks and kitchen lines are cleaned with trailer jetters; sewer cleaning equipment explained describes what each one does.
- Does the service include a full pump-out, including solids, and scraping?
- Will you provide a written service record and hauling manifest for each visit?
- Can you measure and report grease and solids depth before pumping?
- Do you offer line jetting and camera inspection, and can they be scheduled together?
- What are your after-hours rates for service outside business hours?
- How do you handle a blockage between scheduled visits?
Background on grease behaviour is in the fats, oils and grease guide, and cost context is in the sewer cleaning cost guide. To compare providers, request quotes.
FAQQuestions people ask
What is the difference between a grease trap and a grease interceptor?
The terms are often used interchangeably. Grease trap usually means a small unit near the sink that staff clean frequently; grease interceptor usually means a larger tank, often in-ground, that is pumped by a hauler.
What is the 25 percent rule?
A common municipal guideline: service the interceptor when the combined depth of floating grease and settled solids reaches 25 percent of its total liquid depth. Confirm your municipality's threshold.
Can restaurant staff clean the grease interceptor?
Staff often clean small under-sink traps following the manufacturer's instructions. Large in-ground interceptors are pumped by licensed haulers, and nobody should enter an interceptor or its pit because of gas and confined-space hazards.
Do enzyme products replace interceptor pumping?
No. Many municipal programs discourage products that break grease into smaller droplets, because the grease can pass the interceptor and resolidify in the sewer. Mechanical removal is still required.
How often should restaurant kitchen lines be jetted?
Many kitchens jet every three to twelve months, depending on volume, menu and interceptor performance. Recurring slow drains between services are a sign to shorten the interval.
What records should a restaurant keep?
A log of each interceptor measurement and service, the hauler's disposal records, line cleaning invoices, and any camera findings. Keep them for at least as long as your municipality requires.
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