Grease trap maintenance: pump-out frequency, rules and records

“We get it pumped once a year, and the cook pours an enzyme product down the drain every week.” That’s the routine you find under the sink in most restaurants, and it rests on two mistaken beliefs. The first is that grease trap maintenance can be scheduled by the calendar. The second is that a biological product can stand in for a pump-out. In both cases the grease doesn’t go away. It just moves further down the line, into the building drain or the municipal sewer, where it sets up again.

This article is for property managers and building owners who lease space to a restaurant, a bakery or a cafeteria. You’re the one who inherits the basement backup, even if you never fry anything.

When does a grease trap need to be pumped out?

Short answer: pump out a grease interceptor before the floating grease layer and the settled solids, combined, take up 25% of the unit’s liquid volume. That’s the CSA B481 benchmark, and several Canadian cities pair it with a minimum of one service every four weeks. The threshold is measured, not guessed.

That benchmark changes the question entirely. It’s no longer “how many times a year?” but “how many weeks does this kitchen take to hit 25%?” A fry-heavy diner can get there in two or three weeks. An office cafeteria that mostly reheats food may sit well below it after a month. Only repeated measurements give you the right interval for a specific tenant.

Hydromechanical vs. gravity: two devices, two maintenance rhythms

“Grease trap” is the everyday name for two different families of equipment, and their upkeep isn’t planned the same way.

For a hydromechanical unit, the manufacturer usually publishes a grease retention capacity in pounds or kilograms. That number, more than the size of the box, sets the service interval; at least one manufacturer notes that the 25% rule is primarily meant for gravity units and that its hydromechanical models should be serviced against their rated capacity. If your tenant can’t tell you the make, model and capacity, that’s the first piece of information to chase down.

What the Construction Code and By-law 2008-47 actually require

Two texts govern grease interceptors in a Greater Montréal building, and they’re aimed at different people.

The Construction Code, Chapter III, Plumbing. Article 2.4.4.3 requires a grease interceptor wherever a fixture discharging fats, oils or grease sits in a commercial-type kitchen, a restaurant, or a care or detention occupancy, and it must be connected to every fixture that can receive grease. The code points to the CSA B481 series for sizing, location and installation. It governs the work itself: the contractor fitting out the space must comply, as with the rest of the Quebec plumbing code.

Communauté métropolitaine de Montréal By-law 2008-47. Its section 4 b) governs operation: the owner or operator of a restaurant or food-preparation business must route all water likely to contact grease through a grease trap before it reaches the sewer, and must ensure the device is “installed, used and maintained properly.” Enforcement is delegated to member municipalities, and some spell out their expectations. Blainville’s declaration form, for example, requires maintenance and disposal records to be kept for two years. It also prohibits adding emulsifiers, enzymes, bacteria, solvents or hot water to push grease through.

The key word is “or”: owner or operator. If the lease says nothing, the municipality can turn to either one.

Four mistakes that end in a sewer backup

1. The partial pump-out. The contractor skims the visible grease cap but leaves the bottom solids, or returns the decanted water to the tank. Usable volume shrinks with every service. A complete service removes everything, scrapes the walls and checks the baffles.

2. “Miracle” additives. Enzymes and bacteria emulsify grease and carry it into the downstream pipe. A few metres later, the water cools and the grease sets up again. You’ve moved the blockage from a box you can open to a buried line you can’t easily reach.

3. Scalding water. Flushing with boiling water to “clear it out” does the same thing: liquid grease slips through the interceptor and solidifies further along.

4. Missing or misplaced baffles. An interceptor whose outlet baffle was pulled for cleaning and never put back simply lets grease through. It looks clean at every inspection, because it isn’t holding anything anymore.

Longueuil: a clean trap, a plugged drain

A mixed-use building in Longueuil, with a quick-service restaurant on the ground floor and offices upstairs. The property manager called us in January about a backup through the floor drain in the basement mechanical room. The restaurant insisted its hydromechanical interceptor was pumped “every three months,” and had the invoices to prove it.

Opened up, the interceptor held almost no grease. Too little. The outlet baffle was lying beside the unit, removed during an earlier service. On top of that, staff poured an enzyme product down the drain every night. A camera inspection of the building drain showed where the grease had gone: along the stretch running beside the foundation wall, the coldest part of the building in mid-winter, congealed grease had closed off more than half the pipe.

The fix came in three steps: high-pressure jetting of the drain line, reinstalling and securing the baffle, then measuring grease and solids depth every week for a month. Result: the 25% threshold was being reached in just under three weeks. Pump-outs moved to every two weeks, the enzyme product left the kitchen, and a log now hangs beside the sink. At renewal, the lease was amended to spell out who pays for pump-outs and who keeps the receipts. Buildup in the retention pit and its pumps dropped off the following month.

Why a Montréal winter makes it worse

Grease that leaves the interceptor still warm stays liquid for a few metres. In Greater Montréal buildings, the drain line often runs along a foundation wall or through a barely heated crawl space. From December to March, grease congeals faster and closer to the discharge point. An interceptor that was borderline in the fall becomes a backup in February. Winter is the time to measure more often, not less.

The same logic applies at the other end of the kitchen. Grease building up in the hood ductwork is a separate maintenance job, covered in our guide to commercial kitchen exhaust maintenance. A well-run food-service space therefore follows two degreasing schedules, not one.

A one-page log, one measurement a week

The log doesn’t need to be fancy. One page posted near the unit will do:

• make, model, liquid capacity, grease capacity and installation date;
• date of each measurement, floating grease depth, solids depth, percentage of liquid volume;
• date of each pump-out, contractor, volume removed, disposal site;
• condition of the baffles and lid at each opening.

After two months of readings, the right pump-out interval becomes obvious, and you’ll have the proof the municipality can ask for.

This week: ask your tenant for three documents

Email your restaurant tenant and ask for the interceptor’s spec sheet (make, model, capacity), its last three pump-out receipts, and the name of any product being poured down the drains. An incomplete answer tells you where to start.

If the downstream line has never been inspected, do it now, before the deep cold sets in. A camera inspection and an interceptor survey are part of our mechanical plumbing services, and Montréal Combustion can fold the grease interceptor into the building’s maintenance calendar, so a February backup stays a what-if instead of an emergency call.