SNZ Plumbing Estimating · 2026-04-13

Grease Traps for Commercial Kitchens – Sizing & Compliance 2025

Grease trap sizing commercial kitchen, grease interceptor AS/NZS 3500, commercial kitchen plumbing Sydney – full guide for NSW 2025

Grease traps (also called grease interceptors) are mandatory in most commercial kitchens in Australia to prevent fats, oils and grease (FOG) from blocking sewers and causing environmental damage. Incorrect sizing or installation leads to frequent blockages, council fines, Sydney Water penalties and expensive clean-outs.

Here’s everything you need to know from the Plumbing Code of Australia (PCA) and AS/NZS 3500.2:2025 (Sanitary plumbing and drainage) to size and install grease traps correctly in 2025.

When Grease Traps Are Mandatory

PCA Part C2 (Sanitary drainage) and AS/NZS 3500.2 Clause 4.8 (Grease arrestors):

• Required for any commercial kitchen, restaurant, café, takeaway, food court, hotel kitchen, aged care kitchen or food processing facility where fats/oils/grease are generated.
• Exemptions are rare (e.g., very small café with minimal cooking) — most councils/Sydney Water require them for any business with a grease-producing fixture (deep fryer, grill, wok, etc.).
• NSW/VIC/QLD — Sydney Water, Melbourne Water and Queensland Urban Utilities mandate grease traps for new fit-outs or major alterations.

Grease Trap Sizing (AS/NZS 3500.2 Clause 4.8 & Table 4.8.1)

The standard uses fixture unit load and retention time to size grease traps.

Step-by-step sizing:

Calculate total fixture units from all grease-producing fixtures (Table 6.1):

• Commercial sink: 4–6 units
• Dishwasher: 4–8 units
• Grease-producing appliance (fryer, grill): 5–10 units
• Typical small café: 15–30 units
• Medium restaurant: 40–80 units

Minimum capacity from Table 4.8.1:

• Up to 20 units → 200 L
• 21–40 units → 400 L
• 41–80 units → 750 L
• Over 80 units → 1,000 L+ or multiple traps

Retention time — Minimum 90 seconds at peak flow (Clause 4.8.2).

Sydney Water guideline (common in NSW):

• Small takeaway/café: 200–400 L
• Restaurant with fryer/grill: 750–1,000 L
• Large commercial kitchen: 1,500–3,000 L or two-stage system

Installation & Compliance Requirements

• Location: Outside building, accessible for maintenance (pumping every 1–3 months).
• Vent: Vent pipe to atmosphere (Clause 6.10).
• Sampling point: Required for oil/grease monitoring.
• Pump-out: Contract with licensed waste contractor.
• Labelling: "GREASE TRAP – DO NOT DISCHARGE CHEMICALS" signs.

Common Mistakes & Rejections

• Undersizing (e.g., 200 L for a 60-unit kitchen) → frequent blockages & fines.
• No maintenance plan — Sydney Water can issue notices.
• Internal installation (not accessible) → rejected.
• No grease trap on Notice of Work → compliance fail.

Estimating Tips for Sydney Commercial Kitchens

• Small café/takeaway (20–40 units): 400 L grease trap → $1,500–$3,000 (supply + install + concrete pit)
• Medium restaurant (50–80 units): 750–1,000 L → $3,000–$6,000
• Large kitchen (100+ units): 1,500 L+ or two-stage → $6,000–$12,000
• Add annual pump-out contract ($500–$1,500/year) in maintenance quotes.

At SNZ Plumbing Estimating, we size grease traps accurately using AS/NZS 3500.2 Table 4.8.1 and Sydney Water guidelines — no blockages, no fines.

Have you had a grease trap undersized? Share your story or DM us for a quick sizing check on your next commercial kitchen job!

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