Grease Trap Size for a Bar: How to Work Out What You Actually Need

The drain backs up on a Friday night. The smell hits before the plumber does. By the time you find a contractor willing to come out on a weekend, you've already comped three tables and lost a shift's worth of revenue.

For most bar owners, that scenario isn't hypothetical. It's what happens when the grease trap is too small for the load it's handling, or when nobody checked the sizing requirements before the fit-out was signed off.

Getting the size right before you install, or confirming you have the right unit before your next council inspection, saves you all of that.

Why Bars Are a Higher-Risk Category Than Most People Realise

A bar might not look like a heavy grease producer. No deep fryers running all day, no commercial oven cranking out roasts. But grease trap sizing isn't just about cooking oil.

Bars produce fats, oils, and grease (FOG) from a few directions at once. Food preparation areas contribute cooking fats even from basic bar snacks and shared plates. Glass washers and bar sinks discharge detergent-laden water that carries emulsified grease into the drainage system. And if you run a kitchen, even a compact one doing burgers, wings, or loaded fries, the load climbs significantly.

Councils and water authorities in Australia and New Zealand classify food and beverage premises by the nature and volume of their FOG output, not just by whether they identify as a restaurant or a bar. If your bar serves food, your licensing and trade waste agreement will almost certainly require a grease trap that matches the full food-service load, not just the bar side.

The EPA's guidance on fats, oils, and grease management outlines why FOG management is a statutory obligation for commercial food premises in Victoria, and similar frameworks apply in every state and territory.

How Grease Trap Size Is Calculated

Sizing is not guesswork, and it's not a one-size-fits-all table. The calculation is based on the volume of wastewater your fixtures generate during peak operation, expressed as litres per second or litres per minute of flow.

The Flow Rate Method

Most Australian councils and plumbing authorities use a flow-rate method drawn from the Plumbing Code of Australia and the relevant state plumbing standards. Each fixture connected to the trap, pot sinks, bar sinks, glass washers, dishwashers, floor drains, contributes a rated flow. Add them up and the result determines the minimum trap capacity in litres.

As a rough guide, industry bodies note that a single commercial dishwasher typically contributes between 1.5 and 3 litres per second depending on the model and cycle rate. A three-compartment bar sink adds more. A floor drain rated for kitchen washdowns adds more again. The trap needs to hold that combined flow and allow enough retention time for grease to separate from the water before it exits.

The Plumbing Code of Australia (PCA) sets the national framework, and state regulators apply it through their own licensing and inspection regimes.

Fixture Units vs Volumetric Traps

Smaller bars sometimes use an under-sink trap rated in fixture units, a compact unit that handles a limited number of connected fixtures. Larger operations, or any bar with a full kitchen attached, typically require a volumetric interceptor buried in the floor or outside the building, rated in hundreds or thousands of litres.

A bar doing modest trade with a small prep area might qualify for a 45-litre or 100-litre under-bench unit. A bar running a full commercial kitchen during dinner service could need a 1,000-litre or larger in-ground interceptor. The difference in cost, installation, and ongoing pump-out frequency is significant.

For a sense of what that cleaning cost looks like once you know your trap size, see Grease Trap Cleaning Cost 2026: Real Prices by City and Trap Size.

What Determines the Right Size for Your Specific Bar

Your trade waste agreement is the starting point. If your bar is already operating, your local council or water authority will have approved a trap size when your trade waste permit was issued. Pull that document out and check what's written on it, the approved trap volume and the maximum discharge limits.

If you're fitting out a new bar, or the existing trap was approved years ago and your operation has grown since then, the sizing needs to be confirmed by a licensed plumber against your current fixture list.

Key factors that drive the required size

• Number and type of fixtures connected. Each sink, washer, and drain adds to the peak flow rate.
• Seating capacity and peak covers. Higher turnover means more dishwashing cycles, more prep waste, more load through the system.
• Whether you serve food. A drinks-only bar with no kitchen has a materially different load profile than a sports bar running a full bistro.
• Cooking method. Deep frying produces far more FOG than grilling or oven cooking. If you added a fryer since your original fit-out, your existing trap may now be undersized.
• Discharge connection point. Some councils require specific retention times based on how the trap connects to the sewer, which can affect the minimum volume required.

Bars and grills face a specific compliance challenge because they straddle two load categories, see how commercial kitchens handle this for a closer look at what the fixture count means in practice.

When Your Current Trap Is the Wrong Size

There are two failure modes: too small and too large.

Too small is the obvious problem. The trap fills faster than the pump-out schedule allows, solids carry over into the sewer, and you breach your trade waste conditions. Councils can issue infringement notices, require immediate pump-outs at your cost, or revoke your trade waste agreement, which effectively shuts your kitchen down until you comply.

According to Water Services Association of Australia (WSAA) trade waste data, FOG-related sewer blockages cost Australian water utilities tens of millions of dollars annually, which is why enforcement on non-compliant premises has tightened across most major councils.

Too large is less discussed but worth knowing. An oversized trap causes FOG to cool and congeal rather than stay in suspension, which can make it harder to pump and can create a bigger mess at service time. Sizing up dramatically from the required minimum is not a safety buffer, it's a different kind of problem.

If your drains are slow, you're pumping more frequently than your permit specifies, or you've added kitchen equipment since your original fit-out, it's worth having a contractor confirm your current trap is the right size for your current load. See what cafe operators go through with the same sizing questions, the process is similar for bars.

How to Confirm the Right Size Before Your Next Inspection

Talk to a licensed trade waste contractor first

A licensed contractor who works in your council area will know the local trade waste officer's expectations and can walk through your fixture list to confirm whether your current unit is compliant. They do this regularly and can flag problems before an inspector does.

Contractors listed on platforms like GreaseTrapQuotes are vetted and operate in specific territories, see Contractor Territory Pricing | GreaseTrapQuotes for how that works, or if you're a contractor, Apply to Join GreaseTrapQuotes, For Licensed Contractors | GreaseTrapQuotes.

Review your trade waste agreement

Your trade waste agreement specifies the trap size, the pump-out frequency, and the discharge limits you're approved for. If you've changed your operation in any way, added a kitchen, increased seating, installed a fryer, your agreement may need to be updated. Contact your local council's trade waste officer to discuss a variation before an inspection reveals the discrepancy.

New South Wales operators can find trade waste requirements through Sydney Water's trade waste program. Other states have equivalent programs run by the local water authority or council.

Get the sizing confirmed in writing

Whether you're upgrading, installing new, or just checking compliance, get the recommended size from your plumber or contractor in writing. That document protects you if there's a dispute with council, and it gives the next contractor who services the trap useful context.

For bakeries and food producers with similar FOG management questions, the Grease Trap Cleaning for Bakery guide covers how sizing decisions play out in a different but related context.

Get a Quote for Your Bar's Trap Size and Service Schedule

If you're not certain your trap is sized correctly for your current operation, or you want to compare what a compliant pump-out service actually costs for your trap volume, the fastest way forward is to get quotes from licensed contractors in your area.

Get 3 Grease Trap Quotes, describe your bar, your trap size if you know it, and your service history, and local contractors will come back to you with pricing. No obligation, and it takes a few minutes.

Related reading: Restaurant FOG Compliance Requirements: What Australian Operators Actually Need to Do.