Every food business on the Central Coast that discharges to the sewer is required to manage grease effectively. A blocked grease trap or a sewer system overloaded with fats, oils and grease (FOG) creates a problem that doesn’t stay in the kitchen, it backs up, overflows, creates odour complaints and can trigger Council enforcement. This guide covers what grease traps do, how often they need cleaning, what they cost, and how drain maintenance fits in.
The quick answer
Grease traps should be cleaned every 1-4 weeks for high-volume commercial kitchens, and every 2-3 months for smaller operators. Central Coast Council requires grease traps to operate effectively at all times and can inspect or require compliance works. Maintenance is not optional, it’s a licence condition for most food businesses.
What a grease trap does
A grease trap (also called a grease interceptor) is a tank installed in the drain line between your kitchen fixtures and the sewer. Its function is simple: fat, oil and grease (FOG) float. A correctly sized and functioning grease trap:
- Slows the wastewater flow
- Allows FOG to float to the surface and be retained in the trap
- Allows solids to settle to the bottom
- Allows clarified water (largely free of FOG) to discharge to the sewer
Without a grease trap, the FOG that comes from cooking, dishwashing and equipment cleaning goes straight down the drain and into the sewer, where it solidifies, accumulates and blocks pipes, potentially kilometres downstream.
Types of grease traps used on the Central Coast
| Type | Where used | Typical size | Cleaning frequency |
|---|---|---|---|
| Passive hydromechanical grease interceptor (PHGI) | Small cafes, delis, small restaurants | 30-120 L | Weekly to monthly |
| In-ground grease trap | Larger restaurants, clubs, food halls | 500-5,000 L | Monthly to quarterly |
| Automatic grease removal unit (AGRU) | High-volume food courts, hotels | Built-in | Per unit specs (typically weekly) |
The type your business has depends on when the premises were fitted out and what Council approved. Many older Central Coast premises have undersized grease traps from an era of less rigorous food regulation.
How often does a grease trap need cleaning?
The rule of thumb is the “25% rule”: a grease trap should be cleaned before the combined depth of floating FOG and settled solids reaches 25% of the trap’s total liquid depth. In practice:
| Business type | Approximate cleaning frequency |
|---|---|
| Large restaurant or club kitchen (high volume) | Weekly to fortnightly |
| Medium café/restaurant | Monthly to every 6 weeks |
| Small café or takeaway | Every 6-12 weeks |
| Coffee shop with minimal cooking | Every 3-4 months |
| Bakery / production kitchen | Monthly (high FOG from butter, oil) |
These are indicative only. The actual interval depends on your grease trap size relative to your kitchen output. A plumber can assess the right interval for your specific setup.
Central Coast Council and grease trap requirements
Central Coast Council (which administers the former Gosford and Wyong LGAs) requires food businesses to:
- Install and maintain a compliant grease trap or interceptor
- Keep the trap clean and in good working order at all times
- Maintain records of cleaning (some operators are required to document this)
- Not discharge grease-laden waste to the sewer in excess of permitted limits
Council can audit food businesses and issue improvement notices or penalty infringement notices for non-compliance. The sewer conditions on the Central Coast are monitored, and large grease events can be traced back to their source.
If you’re in a multi-tenancy commercial property (such as the Erina Fair precinct or a Gosford CBD building), the grease trap may be shared and managed by the building owner or body corporate. Confirm responsibility before assuming maintenance is covered.
Signs your grease trap needs attention
| Sign | What it means |
|---|---|
| Slow drain in kitchen | Grease trap at or near capacity, or downstream line blocked |
| Odour from kitchen drains | Grease trap overdue for clean, FOG is anaerobic and produces hydrogen sulphide |
| Back-surge through floor drain | Trap has overflowed or downstream sewer is blocked with grease |
| Flies around grease trap area | FOG exposed to air, trap needs cleaning |
| Tenant complaints about odour | Grease trap venting issues or overfull condition |
Don’t wait for symptoms. Set a maintenance schedule and stick to it, it’s far cheaper than emergency drain clearing.
What’s involved in a professional grease trap clean
- Pump-out: A licensed trade waste disposal contractor pumps the trap contents into a tanker for compliant disposal. This waste is classified as liquid trade waste and cannot be dumped down the drain or in landfill.
- Scrape and wash: The trap walls, baffles and lid are scraped and washed. Old grease that has hardened requires physical removal.
- Inspection: The contractor checks the baffles and inlet/outlet fittings are intact. If the trap is damaged, it needs repair.
- Downstream drain check: A responsible contractor will also check that the drain downstream of the trap is flowing freely, a partially blocked downstream drain means the trap overflows sooner.
Grease build-up in commercial drain lines
Even with a functioning grease trap, some FOG passes through into the drain pipes downstream. Over time, this accumulates on pipe walls, reducing bore and creating blockage risk. For commercial food operations on the Central Coast, periodic hydro-jetting of the drain lines from the grease trap to the street sewer is recommended every 6-12 months, depending on the operation.
For properties with old AC cement or clay sewer pipes, consider a CCTV inspection before high-pressure jetting, old pipe walls can be fragile, and jetting at excessive pressure can cause damage.
For persistent grease issues in downstream commercial drain lines, drain relining provides a smoother internal surface that resists grease adhesion better than old clay or AC cement pipes.
Cost guide for grease trap services on the Central Coast
| Service | Typical cost |
|---|---|
| Small PHGI clean and pump (under 100 L) | $120, $280 per service |
| Medium in-ground trap pump and clean (500-1,000 L) | $350, $700 per service |
| Large in-ground trap pump and clean (1,000-3,000 L) | $600, $1,500 per service |
| Commercial drain hydro jet (kitchen to sewer) | $350, $700 per run |
| CCTV inspection of commercial drain line | $350, $700 |
Grease trap compliance for new food businesses on the Central Coast
If you’re opening a new food business or changing the use of an existing premises, you’ll need to demonstrate grease trap compliance to Council. This typically involves:
- Confirming whether an existing grease trap is present and compliant
- Sizing a new grease trap based on your proposed kitchen fixtures and operating hours
- Installing to AS 4058 (grease interceptors) or the hydraulic engineer’s specification
- Getting Central Coast Council trade waste approval before commencing operations
Talk to a licensed plumber who understands trade waste requirements before fitting out your kitchen, retrofitting a grease trap after the fact is always more expensive.
Frequently asked questions
How long does a grease trap clean take? A typical small-to-medium clean takes 30-90 minutes. Large in-ground traps requiring pump tankers can take 2-4 hours.
Do I need to stop trading while the grease trap is cleaned? Not necessarily. Many operators schedule cleans before opening or after close. Small under-sink PHGIs can often be cleaned with minimal disruption to operations.
Can I clean my own grease trap? For very small PHGIs, basic cleaning is manageable by staff. However, the waste cannot be disposed of down the drain, it needs to go in the general waste (for small quantities in solid form) or through a licensed liquid trade waste contractor. Most operators find it easier to have a contractor service the trap.
What happens if my grease trap overflows into the sewer? Grease overflows are a serious matter. Council can take enforcement action including fines. Additionally, you may be liable for the cost of clearing any downstream blockage in the shared sewer if your grease was the cause.
Do cafes in Erina and Gosford need different sized traps? No, trap sizing is determined by your kitchen’s daily volume and fixture count, not your location. The standards are consistent across the Central Coast.
Have a commercial drain or grease trap problem? Book a drain inspection or clearing service.