Getting the grease trap size right is one of the most commonly mismanaged aspects of commercial kitchen compliance in NSW. An undersized trap fills rapidly, requires frequent expensive pump-outs, and creates the risk of fats and grease entering the sewer, an offence under the Protection of the Environment Operations Act. An oversized trap is a wasted capital expense.
If you are setting up, renovating, or buying a food premises in Port Macquarie, Wauchope, or the broader Mid North Coast area, this guide explains exactly how grease trap size is calculated and what Port Macquarie Hastings Council and the local water authority will require.
Why Grease Traps Are Required
Commercial kitchens generate wastewater with a very high concentration of fats, oils, and grease (FOG). When this wastewater enters the sewerage network at elevated temperatures, the FOG is liquid. As it cools in the sewer pipes, it solidifies and adheres to pipe walls, progressively reducing pipe diameter until blockages occur.
FOG blockages in sewers cause sewage spills, which are environmental incidents and can result in prosecution of both the water authority and the business responsible. To prevent this, NSW requires commercial food premises to install and maintain an approved grease interceptor (commonly called a grease trap) before their kitchen wastewater enters the sewer.
Regulatory Framework in NSW
Grease trap requirements for commercial food premises in NSW are governed by:
- AS/NZS 1220:2021, Mechanical grease arrestors (the primary standard for sizing and performance)
- NSW Plumbing and Drainage Act 2011 and the NSW Code of Practice for Plumbing and Drainage (the “Bluebook”), which mandates the AS/NZS standard
- Local council development consent conditions, Port Macquarie Hastings Council may impose specific requirements through DA conditions
- Water authority trade waste agreement, connection to the sewer for commercial food premises requires an approved trade waste agreement with PMHC’s Water & Sewer division that specifies the acceptable quality of wastewater discharge
All of these must be satisfied. Meeting the plumbing standard doesn’t excuse you from the trade waste agreement, and vice versa.
How Grease Trap Size Is Calculated Under AS/NZS 1220:2021
The standard sizing calculation is based on the peak flow rate of wastewater entering the grease trap. The trap must be large enough to detain the wastewater for sufficient time to allow cooling and separation of grease from the liquid.
Step 1: Identify Grease Trap Connections
Not all drainage from a commercial kitchen goes through the grease trap, only fixtures that generate FOG-laden wastewater:
- Cooking equipment drains (fryers, grills, cooking kettles)
- Pre-wash sinks and dishwasher wastewater
- Floor drains in cooking areas
- Cooking equipment ventilation hood condensate
Fixtures that typically do NOT connect to the grease trap:
- Hand wash basins
- Toilets and urinals
- Bar sink (if no food preparation)
- Normal washbasins
Step 2: Calculate Peak Flow Rate
The peak flow rate from each connected fixture is determined using the fixture unit values in AS/NZS 1220:2021. Each fixture type has a nominal drainage rate. The total flow rate (in litres per minute) represents what the grease trap must handle at peak use.
The standard provides two calculation methods:
Flow rate method: Based on the sum of flow rates from connected fixtures. Empirical method: Based on meal count and food service type, useful for new premises where fixture details are not yet finalised.
Empirical Sizing by Meal Count
For new premises, the empirical method in AS/NZS 1220:2021 uses the following approximate sizing table:
| Meals per Day | Minimum Grease Trap Capacity |
|---|---|
| Up to 50 meals | 1,000 L |
| 50-100 meals | 1,500 L |
| 100-200 meals | 2,000-3,000 L |
| 200-500 meals | 4,000-6,000 L |
| 500-1,000 meals | 6,000-10,000 L |
| 1,000+ meals | Engineer’s assessment |
These are indicative figures. The actual sizing depends on the specific menu (high-fat menus require larger traps), the kitchen equipment configuration, and whether a mechanical FOG separator or high-temperature rinse is used (which reduces FOG load).
Practical Examples in the Port Macquarie Context
Small café, Port Macquarie CBD (50-70 meals/day) Fixtures: 2-bay sink, 1 dishwasher, 2 cooking equipment drains Indicative grease trap size: 1,000-1,500 L Location: Under kitchen floor or in accessible outdoor pit
Mid-scale restaurant (150-250 meals/day) Fixtures: 3-bay sink, commercial dishwasher, fryer drains, grill drain, floor drains Indicative grease trap size: 3,000-4,500 L Location: Outdoor pit, accessible for pump-out
Commercial takeaway with drive-through (300+ meals/day) Fixtures: Multiple fryers, commercial dishwasher, extensive floor drainage, pre-wash bay Indicative grease trap size: 5,000-8,000 L May require: Automatic grease removal unit (AGRU) as supplement to passive trap
Pub/club kitchen (variable, 200-600 meals/day with peaks) Peak flow rate calculation essential. Design size typically 4,000-8,000 L. Trade waste agreement with PMHC Water & Sewer required specifying maximum FOG concentrations in discharge.
Grease Trap Types Approved in NSW
| Type | Description | Suitable For |
|---|---|---|
| Passive gravity trap (concrete) | Concrete pit; FOG floats, solids settle, liquid flows through | Most commercial applications; large capacities |
| Passive gravity trap (poly) | Prefabricated poly unit; faster installation | Smaller cafés and food premises |
| Automatic grease removal unit (AGRU) | Mechanically skims FOG continuously; smaller footprint | Space-constrained kitchens, high-volume operations |
| In-sink grease trap | Small unit fitted under a single sink | Very small food premises, low FOG volume only |
AGRUs (automatic removal units) have a smaller footprint and remove grease continuously rather than accumulating it for pump-out. They are increasingly common in space-constrained urban sites in Port Macquarie where access for a large pump-out vehicle is difficult. However, AGRUs have higher purchase and maintenance costs and require a collection system for the separated grease.
Installation Requirements
All grease trap installations must be:
- Installed by a licensed plumber
- Approved under a plumbing works permit
- Inspected at pre-cover and final stages
- Connected ahead of sewer entry
The grease trap must be accessible for pump-out by a liquid waste vehicle. Minimum access requirements include:
- Lid opening sufficient for the pump-out hose (typically 450 mm minimum)
- Vehicle access to within 30 m of the trap (pump-out hoses have practical length limits)
- Clear overhead access (no structural obstructions above the lid)
Site access issues are common for premises in Port Macquarie’s older commercial building stock. If vehicle access is problematic, discuss options with your pump-out contractor before installation, the trap location may need to be planned around pump-out logistics.
Pump-Out Frequency and Compliance
A correctly sized and regularly pumped grease trap is a compliant grease trap. An oversized trap that is rarely pumped, or an undersized trap that overflows, both create compliance problems.
The pump-out schedule should be based on how quickly the trap fills, typically when accumulated FOG reaches 25-30% of trap capacity. For properly sized traps in busy kitchens:
- High-volume restaurants/takeaways: monthly pump-out
- Standard restaurant (100-200 meals/day): 6-8 weekly pump-out
- Café/small food premise: 8-12 weekly pump-out
We take enquiries for commercial grease trap cleaning and commercial grease trap service contracts for food businesses across Port Macquarie, Wauchope, Camden Haven, and the Mid North Coast region. Regular contracted service ensures your trade waste compliance is maintained without last-minute emergency scrambles.
FAQ
Who approves the grease trap size for my new restaurant? The size is calculated by a licensed plumber or hydraulic engineer based on AS/NZS 1220:2021 and submitted as part of the plumbing approval. PMHC’s Water & Sewer division may also have input through the trade waste agreement process. Your licensed plumber manages this process.
Do I need a grease trap if I’m on septic, not sewer? If your commercial kitchen discharges to an onsite septic system rather than the sewer, a grease trap is still strongly recommended and may be required by your DA conditions. Fats, oils, and grease entering a septic tank significantly disrupt biological treatment and rapidly clog leach fields.
My grease trap is full and I have a health inspection tomorrow, what do I do? Send an urgent enquiry for an emergency grease trap pump-out; commercial food premises emergencies are exactly what that service exists for.
My new café has a small kitchen, do I still need a grease trap? If your premises prepares food that involves cooking with oil or fat, even a small menu, the answer is almost certainly yes. Contact Port Macquarie Hastings Council and your licensed plumber to confirm requirements for your specific menu and fixture configuration.
What concentration limits apply to my grease trap discharge to sewer? Your trade waste agreement with PMHC specifies the maximum FOG concentration (typically 50-150 mg/L) and temperature (typically ≤38°C) at which your wastewater can enter the sewer. Exceeding these limits can result in trade waste agreement cancellation and loss of sewer connection.
Need a grease trap pump-out, service contract, or advice on the right trap size for your Port Macquarie food business? Send an enquiry; grease trap work for commercial kitchens is covered right across the Mid North Coast region.