A composting toilet combined with a greywater treatment system can replace a conventional septic on suitable properties in NSW. This combination is particularly popular with off-grid and eco-minded property owners in the Comboyne, King Creek, and Hastings hinterland areas who want to avoid the ongoing cost of septic pump-outs and the installation complexity of an AWTS on constrained or remote sites.
The key point upfront: in NSW, a composting toilet with a greywater management system is a legitimate alternative to a conventional septic, but it still requires Council approval, it requires proper maintenance, and it is not a set-and-forget system. Failing to manage either component properly creates health risks and Council compliance issues.
How the Combined System Works
The Composting Toilet
A composting toilet processes human waste (faeces and urine) on-site through aerobic decomposition rather than flushing it into a septic tank. The end product is a dry, soil-like compost that is hygienically safe when properly managed.
There are two main types:
Self-contained composting toilets: The composting chamber is integrated into the toilet unit, usually installed above the floor. Suitable for small cabins, tiny homes, or where minimal wastewater flow is expected.
Remote/central composting systems: The toilet itself looks like a standard pedestal but waste drops via a chute to a large composting chamber installed in a basement, beneath the floor, or outside the dwelling. Greater capacity, suitable for permanent residences and families.
Key operating requirements:
- Carbon material (sawdust, wood shavings, paper) added after each use to balance nitrogen and moisture
- Regular turning/aeration of the composting mass
- Temperature management (the composting process benefits from warmth)
- Liquid (leachate) management, most systems have a drain for excess liquid which must be managed separately
The Greywater System
A composting toilet eliminates blackwater (toilet waste) but the property still generates greywater from showers, baths, basins, and laundry. This must be managed through a separate greywater treatment or disposal system.
Options for the greywater component:
- Simple greywater diversion to garden (Tier 1, no approval), only suitable for very basic/minimal use situations
- Greywater treatment unit (approved), biological treatment + dispersal
- Full greywater treatment system with Council approval, allows more flexibility in application
In most permanent residence situations, Council will require an approved greywater treatment system with engineered dispersal, not just a laundry-to-lawn hose.
NSW Regulatory Position
Composting toilet + greywater systems are approved under NSW Government’s framework for onsite sewage management. They are listed as a compliant alternative in AS/NZS 1547:2012.
To install a composting toilet system as an alternative to conventional septic in the Port Macquarie Hastings LGA:
- The composting toilet model must be listed on the NSW Health product approval register
- The greywater management component requires Council approval via a DA
- A site assessment must confirm the greywater component’s feasibility (soil, setbacks, area)
- Ongoing maintenance records must be kept
Not all composting toilet models are NSW-approved. Check the NSW Health website for the current list of approved models before purchasing. Installing an unapproved unit can result in Council requiring its removal.
Is This System Right for Your Property?
Good Candidates
| Property Type | Why It Works |
|---|---|
| Off-grid or remote rural block (Comboyne, Upper Hastings) | No septic pump-out truck access, limited water supply, minimal greywater generated |
| Small eco-cabin or cabin retreat | Low usage, owner committed to ongoing maintenance |
| Steep blocks with poor soil (Hastings ranges) | Difficult to install conventional absorption area |
| Properties with extremely high water table | Composting toilet avoids wastewater going into saturated ground |
| Owners who want to minimise water use | No water used in toilet flushing |
Poor Candidates
| Property Type | Why It May Not Work |
|---|---|
| Permanent large family home | Composting capacity must match load, large systems required |
| Properties with tenant or visitor turnover | Composting toilet operation requires informed, willing users |
| Properties where owners are frequently absent | Composting process requires monitoring and management |
| Holiday rentals with guest changeovers | Guests unfamiliar with composting toilets can misuse them, creating failures |
What Maintenance Does a Composting Toilet Require?
A composting toilet is not a “put it in and forget it” system. Ongoing maintenance is what makes the difference between a well-functioning system and a foul-smelling disaster.
Regular (weekly to monthly):
- Add carbon material (sawdust/wood shavings) as needed to maintain balance
- Turn or aerate the composting mass if the system requires manual turning
- Check moisture level, too wet causes odour and anaerobic conditions; too dry slows decomposition
- Monitor liquid drainage and ensure leachate outlet is clear
Seasonal (every 6-12 months):
- Remove finished compost from the base of the unit
- Inspect the unit for structural integrity and seals
- Clean ventilation system and check fan operation (most units have electric ventilation)
- Inspect greywater treatment system
End product use: Finished compost from an approved composting toilet can be used in gardens and on land (not directly on food crops, and usually not on vegetable gardens without a further curing period). Check your specific Council approval conditions.
Common Problems With Composting Toilets in NSW
Too Much Liquid (Overwetting)
Urine volume typically exceeds faecal volume, and if not managed, excess liquid creates anaerobic conditions in the chamber, which causes strong odour (hydrogen sulphide, ammonia) and slows decomposition. Systems with a urine diverter that separates liquid from solids at the bowl avoid this problem.
Odour Issues
A properly operating composting toilet in a well-ventilated installation should have minimal odour inside the dwelling. Odour problems almost always trace to:
- Incorrect carbon:nitrogen balance (add more sawdust)
- Inadequate ventilation (check fan and vent pipe)
- Overwetting (too much liquid)
- Underuse (not generating enough heat for active composting)
Not Reaching Composting Temperature
Effective pathogen reduction requires the composting mass to reach and sustain 55°C+ for a period. In the cooler months of the Hastings ranges (Comboyne can have cold winters), the composting process slows significantly. Some systems use small electric heating elements to maintain temperature. Others rely on adequate retention time (typically 12+ months) rather than temperature.
Greywater System Failure Causing Odour
Even if the composting toilet is working well, a blocked or overloaded greywater system can produce odour and surface pooling. The two components of the system must both be maintained.
Costs for a Composting Toilet + Greywater System
| Component | Indicative Cost (2026 AUD) |
|---|---|
| Composting toilet unit (small self-contained) | $1,800 to $3,500 |
| Composting toilet unit (full residential remote system) | $5,000 to $10,000 |
| Installation (building works, chute, ventilation) | $2,000 to $5,000 |
| Greywater treatment system | $3,000 to $8,000 |
| Greywater land application area | $2,000 to $5,000 |
| Council approval and design | $1,500 to $3,000 |
| Total indicative range | $15,000 to $31,500 |
Compare this to a conventional AWTS system ($18,000 to $28,000), the costs are broadly comparable for a full system, though the ongoing maintenance costs of a composting system are lower if managed properly (no quarterly AWTS service fees, no pump-outs).
Comparing Composting Toilet + Greywater vs AWTS
| Factor | Composting Toilet + Greywater | AWTS + Drip Irrigation |
|---|---|---|
| Installation cost | $15,000 to $31,500 | $18,000 to $28,000 |
| Annual maintenance cost | $200 to $500 (DIY-maintainable) | $800 to $1,500 (quarterly service required) |
| Council quarterly service requirement | No | Yes |
| Power requirements | Low (ventilation fan only) | Moderate (aerator + pump) |
| User involvement required | High (ongoing carbon addition, turning) | Low |
| Suitable for holiday rentals/tenants | Difficult | Generally yes |
| Water savings | High (no flush water) | Nil |
FAQ
Can I install a composting toilet on any rural property near Port Macquarie? Subject to Council approval and the site being suitable for the greywater management component, yes. The composting toilet model must be NSW Health approved and the greywater system must be able to meet all required setbacks. Contact Port Macquarie Hastings Council for pre-DA advice.
Is the compost from a composting toilet safe? Properly composted output from an approved system, after adequate retention time and reaching correct temperatures, is hygienically safe and pathogen-free. It is classified as a beneficial soil conditioner. NSW Health provides guidance on safe use of composting toilet end product.
Do composting toilets smell inside the house? A well-maintained composting toilet with correct ventilation should not produce noticeable odour inside the dwelling. The fan creates negative pressure in the toilet compartment, drawing air away from the room and through the composting chamber to the vent stack. Persistent odour indicates a maintenance issue.
Can I use a composting toilet in a house that is rented out to tenants? It is possible but requires careful tenant selection and clear instructions. Tenants who don’t understand the system (not adding carbon material, flushing inappropriate items) can quickly create problems. Many landlords of composting toilet properties have a handover induction as a condition of tenancy.
What happens to the greywater from a composting toilet property? Greywater from showers, laundry, and basins must still be managed through an approved greywater treatment or septic system, the composting toilet only eliminates the toilet waste (blackwater). See our guide on greywater reuse in NSW for the options.
Thinking about a composting toilet system for your rural Mid North Coast property? Contact us for advice on what works in your area and what Council approval requires.