Quick answer. A container restaurant in Ontario almost always needs a hydromechanical grease interceptor sized to the three-compartment sink flow rate, calculated as length x width x depth x compartment count, divided by 231 (cubic inches to gallons), multiplied by 0.75 displacement, drained in 1 minute. For a typical 18 x 18 x 10 inch three-bay sink that lands at 35 GPM, rounded up to the next CSA B481.1 certified size.
The grease trap discharges through a 1.5 inch vent tied into the plumbing venting system, sits as close to the sink as physically possible inside the container, and gets pumped by a Ministry of the Environment, Conservation and Parks certified hauler every four weeks or before the 25 percent fill mark, whichever lands first. A container restaurant is held to the same grease-handling standard as any brick-and-mortar food premises. Costs, sizing math, vent layout, and what the kitchen plumbing rough-in we recommend looks like in steel sit below. The LeBlanc family has run Van Blanc Ent. Inc. since 1995. 124+ verified Google reviews at 4.9 stars, 1-3 day delivery.
In This Guide
- Why is the grease trap the most-failed inspection in container kitchens?
- How do you size a grease trap by GPM?
- What size grease trap does a three-compartment sink need?
- Where does the grease interceptor go inside a 20 ft or 40 ft kitchen?
- How do you vent a grease interceptor in a container kitchen?
- What slope and cleanouts does the drain line need?
- How often does a grease trap need to be pumped out?
- What drives the cost of a container grease trap system?
- What rough-in mistakes fail a health inspection?
- Christian on what we tell every container restaurant buyer
- Frequently asked questions
Reading time: about 14 minutes.
Why is the grease trap the most-failed inspection in container kitchens?
A grease trap, also called a grease interceptor, is the device that fails container-kitchen inspections most often because it has to be sized by flow rate, vented on the outlet side, and placed within about 8 feet of the sink, and contractors routinely miss one of those three. Get the sizing math right first and the rest follows.
Every Ontario container restaurant operator we have delivered a 20 ft or 40 ft food-service shell to in the past decade has run into the same three plumbing items at inspection: handwash placement, three-compartment sink venting, and the grease interceptor. The first two are usually fixed at the contractor stage. Any fixture discharging sewage containing fats, oils, or grease where food is cooked, processed, or prepared has to discharge through a grease interceptor. No exemption for small or container-built operations. Inside a container the space premium is real. A 20 ft food-service shell has roughly 160 square feet before the cookline, prep tables, hood, and walk-in cooler claim their share. The trap fits under the three-compartment sink or against the wall behind it. Settle that detail as part of planning a shipping container kitchen build before any contractor cuts a hole in the floor.
Paul LeBlanc, owner of Van Blanc since 1995: “I have watched container kitchen builds for years out of our Brantford yard, and the grease trap is where the cheap quotes catch up with people. A contractor who sizes it by seat count to win the job hands you a trap that overflows in week three. We tell every buyer to settle the trap, the vent, and the floor cut at the yard before the steel ships. It is the one conversation that saves a re-inspection.”
How do you size a grease trap by GPM?
Grease interceptor sizing in Ontario follows CSA B481.3. The formula is simple arithmetic and worth knowing before you talk to a contractor, because some round in the wrong direction and you end up with an undersized trap that overflows in week three.
The CSA B481.3 sizing arithmetic
Step 1: Multiply length x width x depth of each sink compartment, in inches, to get cubic inches.
Step 2: Multiply by the number of compartments served by the same drain line.
Step 3: Divide total cubic inches by 231 to get capacity in US gallons.
Step 4: Multiply by 0.75 to adjust for actual usable capacity.
Step 5: Divide by drain time in minutes. Default is 1 minute. Most Ontario AHJs hold to that.
Step 6: Round up to the next available CSA B481.1 certified size. Common sizes are 7, 10, 15, 20, 25, 35, 50, and 75 GPM. Never round down.
The seat-count formula that some municipalities reference back-calculates trap size from meal count. It usually produces a smaller number than GPM. Size by GPM regardless. It is the only formula that survives a peak-hour washdown of three full sink bays at once.
What size grease trap does a three-compartment sink need?
A three-compartment sink is the fixture that sets your grease trap size, and most Ontario container restaurants use a standard NSF-certified one. The 18 by 18 by 10 inch bowl is the workhorse. High-volume dish work sizes up to 20 x 20 x 12. Here is what each configuration produces.
| Bowl size (LxWxD inches) | Cubic inches per bowl | Total (3 bowls) | USG capacity | x 0.75 displacement | GPM at 1 min | CSA size to install |
|---|---|---|---|---|---|---|
| 16 x 16 x 8 | 2,048 | 6,144 | 26.6 | 20.0 | 20.0 | 20 GPM |
| 18 x 18 x 10 | 3,240 | 9,720 | 42.1 | 31.6 | 31.6 | 35 GPM |
| 18 x 18 x 12 | 3,888 | 11,664 | 50.5 | 37.9 | 37.9 | 50 GPM |
| 20 x 20 x 12 | 4,800 | 14,400 | 62.3 | 46.8 | 46.8 | 50 GPM |
| 24 x 24 x 14 | 8,064 | 24,192 | 104.7 | 78.5 | 78.5 | 75 GPM (verify with AHJ) |
The 18 x 18 x 10 bowl lands the 35 GPM trap as the correct CSA size. A 35 GPM hydromechanical interceptor weighs about 80 to 110 pounds dry, fits in a 24 inch deep cabinet, and connects to a 3 inch drain inlet and 3 inch outlet. That is the spec you give your contractor, not a vague request for a standard grease trap. Vague requests come back as 20 GPM units that fail inspection.
Pro tip from our delivery yard
The dishwasher should NEVER discharge into the grease interceptor. Dishwashers run at 140 to 180 F, and that heat liquefies the grease in the trap and lets it pass straight through to the sewer. CSA B481.3 explicitly excludes dishwasher waste from grease trap influent. Run the dishwasher to its own indirect drain to the floor drain, then to the building drain downstream of the interceptor.
Where does the grease interceptor go inside a 20 ft or 40 ft kitchen?
A grease interceptor inside a container kitchen has three viable locations, each with tradeoffs. Past that distance, grease cools, congeals, and clogs the drain line before it ever reaches the trap.
Location 1 is directly under the three-compartment sink, inside the sink cabinet. Standard for compact 20 ft kitchens. The trap sits between the sink bottom and the container floor, with 18 to 24 inches of vertical room. Pump-out access is through the front cabinet door.
Location 2 is in a recessed pit cut into the container floor, accessible through a stainless steel access plate flush with the kitchen floor. Cleanest installation for a 40 ft restaurant. The floor cut has to be reinforced because the container floor is structural, which is one of the cuts and reinforcements we do at the yard before the container ships.
Location 3 is exterior to the container, mounted on a concrete pad alongside, with the drain line passing through a sealed sleeve in the side wall. Works for permanent installations parked long-term. Worst option for mobile or pop-up container restaurants because relocating means disconnecting and resealing.
What we see from our Brantford yard
Most container restaurant buyers we deliver land on Location 1 (under-sink) for 20 ft kitchens and Location 2 (recessed pit) for 40 ft. Location 3 shows up on stationary food-court installations like Toronto’s Market 707. Christian walks every buyer through the location decision before the container ships, because the floor cut for Location 2 has to happen at the contractor yard, not the operating site.
How do you vent a grease interceptor in a container kitchen?
A grease interceptor is vented from its outlet side under the Ontario Building Code plumbing provisions, never from the inlet. Get the vent connection point wrong and the trap stops separating grease. These are the vent rules that matter for a container kitchen:
- Vent size. At least 1.5 inches diameter, connected to the outlet side. Most contractors run a 2 inch vent because it ties more cleanly into the main stack.
- Connection point. Outlet side only, downstream of the grease retention chamber. Venting the inlet defeats the trap.
- Termination. Through an approved roof flashing, at least three feet above the roof line if the roof is occupied or accessible, six inches if it is not.
- Wet venting. Permitted under OBC 7.5.2.1 for some fixtures but not for grease interceptors. The grease contaminates the vent flow.
- Sealing. The roof penetration has to be sealed against weather with EPDM boot or lead flashing, and reinforced if the corrugation runs through the cut.
Venting is the second-most-failed inspection item after grease trap sizing. The most common failure is contractors running the vent to the inlet side because that is where the rough-in stub already lives. Fix is moving the connection to a tee on the outlet side. Two hours of plumber time at install prevents a re-inspection. The grease vent is a separate run from the cooking exhaust, so plan it alongside the hood and makeup-air sizing rather than after it.
What slope and cleanouts does the drain line need?
The drain line in a container kitchen runs sink to grease trap to building drain to either municipal sewer or holding tank. Each segment has slope, sizing, and cleanout requirements.
| Drain line segment | Minimum diameter | Required slope | Cleanout spacing |
|---|---|---|---|
| Sink trap arm to floor drain or trap inlet | 2 in (1.5 in for single-bay) | 1 in 50 (1/4 in per ft) | at each direction change |
| Floor drain to grease interceptor inlet | 3 in | 1 in 50 | at trap inlet |
| Grease interceptor outlet to building drain | 3 in | 1 in 50 | at outlet, 15 m max spacing |
| Building drain to municipal connection | 4 in | 1 in 50 | at exterior wall, every 15 m |
| Vent stack (outlet side of trap) | 2 in | vertical | n/a |
The 1 in 50 slope (about 1/4 inch per foot, or 2 percent) is the OBC minimum for drainage pipes under 3 inches. Anything shallower allows solids to settle in the pipe. Anything steeper than 1 in 25 causes water to outrun solids and produces the same clogging from the opposite direction. Cleanouts go at the grease trap inlet, the outlet, and at every change of direction greater than 45 degrees. Brass cap, hex head, sealed with thread sealant.
How often does a grease trap need to be pumped out?
A grease trap in Ontario requires pump-out before grease and solid contents combined reach 25 percent of trap liquid volume, or every four weeks, whichever comes first. Most container restaurants land on the four-week cadence because the 25 percent fill line is hard to verify between visits.
Pump-out has to be performed by a Ministry of the Environment, Conservation and Parks (MECP) certified waste hauler. The hauler arrives with a vacuum truck, pumps the contents, scrapes the residual grease off the baffles, refills with clean water to restore the seal, and signs a manifest. Keep the manifest on file at the restaurant. The health unit inspector will ask for it first.
| Service cadence | What drives the per-visit cost | Risk profile |
|---|---|---|
| Every 2 weeks (high-volume kitchens) | More visits per year, so the highest annual spend, but a smaller, faster pump each time | Lowest risk, highest cost |
| Every 4 weeks (standard QSR) | The industry baseline cadence most haulers price against; predictable monthly line item | Industry baseline, code-compliant |
| Every 6-8 weeks (low-volume only) | Fewer visits, but each pump removes more accumulated grease and takes longer | Requires fill monitoring, AHJ approval |
| Quarterly or longer | n/a | Non-compliant under Ontario standards |
The four-week cadence sets the recurring pump-out line item, and that belongs in any container restaurant pro forma. Operators who try to stretch the schedule to save money end up paying more on emergency callouts when the trap overflows and the line backs up into the kitchen floor drain. Same-day shutdown event.
What drives the cost of a container grease trap system?
The grease trap system in a container restaurant carries a one-time install cost plus an ongoing pump-out cost, and the line items below are what move each one up or down. There are no fixed numbers worth quoting here because trap size, install location, and which municipal fees apply change the total on every build.
| Line item | Applies to | What drives the cost up or down |
|---|---|---|
| Hydromechanical grease interceptor (35 GPM stainless steel) | 20 ft and 40 ft builds | GPM rating, stainless vs coated steel, CSA B481.1 certification |
| Larger trap (50-75 GPM for high-volume) | 40 ft and high-volume only | Higher flow rating and larger retention chamber cost more than a 35 GPM unit |
| Plumber rough-in (drain, vent, fittings) | 20 ft and 40 ft builds | Number of fixtures, vent runs to the roof stack, and licensed-trade hours |
| Floor cut and weld reinforcement (if Location 2 pit installation) | Mostly 40 ft recessed-pit builds | Structural floor cut plus welded reinforcement; skipped entirely for under-sink installs |
| Exterior pad and sleeve (if Location 3 exterior installation) | Stationary long-term parks | Concrete pad size and the sealed side-wall sleeve penetration |
| Municipal building permit for grease interceptor (Toronto, Hamilton) | Municipalities that require it | Set by each municipality; Toronto and Hamilton charge more than smaller AHJs |
| Health unit plan review and inspection fee share | All food premises | Plan-review scope and number of re-inspections if items fail |
| Annual pump-out service (4-week cadence) | Ongoing, all builds | Trap volume, visit frequency, and hauler travel distance to your site |
| One-time install cost | Higher for 40 ft | Trap size, install location, and which permits apply |
| Annual operating cost | Higher for 40 ft | Pump-out cadence and trap volume |
Across a three-year window the grease system runs higher for a 40 ft restaurant than a 20 ft kitchen, but as a share of the total it usually lands around 5 to 12 percent of build cost and it is non-negotiable. Fold it into the same line as the rest of your container build budget from day one.
What rough-in mistakes fail a health inspection?
The rough-in mistakes that fail a container kitchen inspection come down to five errors we see most often when container restaurant buyers come back to us asking why they failed their pre-opening inspection. Every one of them is preventable at the contractor stage.
- Trap sized by meal-count instead of GPM. Contractor uses the seat-count formula because it produces a smaller number and a cheaper trap. Inspector recalculates using GPM and fails the install. Fix: size by GPM, round up, document the math.
- Vent connected to the inlet side. Easier rough-in but defeats the grease separation chamber. Fix: vent has to tie into the outlet side, downstream of the retention baffle.
- Dishwasher discharging through the interceptor. Hot water liquefies the grease and passes it through. Fix: dishwasher gets its own indirect drain to the floor drain, downstream of the trap.
- Trap installed more than 8 ft from the sink. Grease cools and clogs the drain line before reaching the trap. Fix: relocate trap closer to fixture, or add a smaller pre-trap at the fixture itself.
- No pump-out manifest on file. Health inspector asks for the most recent service record. Operator cannot produce one. Fix: set up the MECP-certified hauler contract before opening day, keep manifests in a binder at the kitchen.
Christian on what we tell every container restaurant buyer
Christian LeBlanc, second-generation operator at Van Blanc: “Every container restaurant buyer who walks our Brantford yard asks the same first question: can I just put a sink in this 20 ft bin and call it a kitchen. The answer is yes, but the trap, the vent, the floor cut, and the hauler contract have to happen at the contractor yard before the container ships. The contractors who do this work right cost the same as the ones who do it wrong. The difference is the ones who do it right ask us about the floor cut and the side-wall sleeve before they quote. That is how you tell.”
Frequently asked questions
Do I really need a grease trap in a small 20 ft container kitchen?
Yes. No exemption for small or container-built operations. The health unit will not issue an operating permit without one.
Can I use a small under-sink grease trap instead of a full interceptor?
For a single-bay handwash sink, sometimes yes. For a three-compartment dishwashing sink, no. The 4 to 8 GPM under-sink units are designed for single-fixture low-volume applications. A three-bay sink peak-hour wash easily hits 30 to 40 GPM and overwhelms them.
How long does the grease trap install take at the contractor yard?
Two to three days inside a 20 ft container kitchen, three to five days for a 40 ft. Permit inspection adds another two to seven days. Plan four to six weeks from container delivery to inspection sign-off if everything goes smoothly.
Who installs the grease trap, the container supplier or the plumber?
The plumber. Van Blanc delivers the container including any side-wall sleeve cuts or floor reinforcement agreed at the yard. The trap, rough-in, vent stack, and sewer connection are licensed plumbing work for an Ontario certified tradesperson. Confirm commercial kitchen experience before signing.
What happens if my container restaurant relocates? Do I have to reinstall the trap?
Yes. The interceptor is plumbed to the building drain at the operating site. When the container moves, the connection breaks. At the new site you need a fresh plumbing permit, fresh inspection, and a new MECP-certified hauler contract.
Can the dishwasher and the prep sink share the same grease interceptor?
The prep sink yes, the dishwasher no. CSA B481.3 excludes dishwasher discharge because 140 to 180 F water liquefies captured grease and lets it pass through. Run the dishwasher to a separate indirect floor drain downstream of the trap.
How do I size the trap for a container food truck with no fixed sewer?
Size by CSA B481.3 GPM math the same way. The trap discharges into a holding tank instead of a sewer. The tank gets pumped by an MECP-certified hauler every four weeks or before 75 percent capacity. Most food trucks use 75 to 150 gallon greywater tanks.
What CSA standard do I need to ask the contractor for?
Three. CSA B481.0 covers material and construction. CSA B481.1 (lard test) or B481.2 (oil test) covers performance rating. CSA B481.3 covers sizing and installation. Confirm the trap has a physical CSA B481.1 certification mark on the unit, not just the cut sheet.
Does the grease trap have to be inside the container or can it sit outside?
Either works. OBC 7.4.4 requires the trap as close as possible to the fixture, so the sink-to-trap drain run should not exceed about 8 feet. Under-sink, recessed floor pit, and pad-mounted exterior with a sealed sleeve all meet that. Mobile kitchens favour interior locations.
How much does the whole grease management system cost in a container build?
There is a one-time install cost that covers the trap, rough-in, floor cut, permits, and inspection fees, and it runs higher for a 40 ft restaurant than a 20 ft kitchen. On top of that sits the annual pump-out service. Over a three-year window the whole grease system typically works out to roughly 5 to 12 percent of build cost, driven mostly by trap size, install location, and which municipal permits apply.
Reach Van Blanc in Brantford
Van Blanc has been supplying shipping containers across Ontario since 1995. Our yard is at 90 Morton Avenue East in Brantford. We have delivered to dozens of container restaurant builds over the past decade, and we walk every food-service buyer through the plumbing rough-in conversation before the container ships. If you are still weighing what a steel box can become, our overview of turning a bin into a working kitchen or cafe covers the build options. The trap, the vent, the floor cut, the side-wall sleeve, and the pump-out hauler contract are all the operator’s responsibility, but the spec sheet gets agreed to here at the yard so your contractor knows what they are working with.
Van Blanc Ent. Inc. · 90 Morton Ave E Unit 1B, Brantford, ON N3R 7J7 · +1 888-509-6658
Drive out and walk the yard with us before you commit to a 20 ft or 40 ft container restaurant build. Worth the drive for unbeatable quality and 30 years of family customer service. Every quote comes with a real lead time, not a hopeful one.
Placement requirements vary by municipality. A quick call to your local planning office before delivery is the easiest way to confirm what works for your property.
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