Installing a septic tank is a significant investment for any Auckland homeowner, especially for those in rural or off-grid properties where a connection to the main sewer system isn’t an option. A properly installed septic system provides long-term, hassle-free wastewater treatment. However, if mistakes are made during installation, homeowners could face costly repairs, environmental contamination, and even legal trouble.
In this guide, we’ll cover the most common mistakes made when installing a septic tank and how to avoid them. Whether you’re considering a DIY installation or hiring a professional, these insights will help ensure your septic system runs efficiently for years to come.
Choosing the Wrong Septic Tank Size
Many homeowners assume that any septic tank will do, but choosing the wrong size can lead to major issues. A one-size-fits-all approach does not work because the required tank size depends on multiple factors:
- The number of people living in the household.
- The amount of daily wastewater generated.
- The number of plumbing fixtures and appliances.
How to Determine the Correct Size
New Zealand regulations outline septic tank size based on the number of bedrooms. A general rule of thumb:
- 1-2 bedrooms: 3,000L minimum.
- 3-4 bedrooms: 4,500L minimum.
- 5+ bedrooms: 6,000L minimum.
An undersized septic tank fills too quickly, causing frequent backups and the need for constant pumping. An oversized tank may not allow for proper bacterial breakdown of waste, leading to odours and inefficiencies.
Solution: Work with a septic system professional to calculate your household’s wastewater needs and choose an appropriately sized system.
Ignoring Soil and Site Conditions
Septic tanks rely on natural soil filtration for wastewater treatment. If installed in the wrong soil type, the system may fail to drain properly or risk contaminating groundwater.
Common Soil-Related Mistakes
- Not conducting a percolation test – This test determines how well soil absorbs and filters water.
- Installing in clay-heavy soil – Clay retains water and prevents proper drainage, leading to pooling and backups.
- Overlooking high water table areas – If groundwater is too close to the surface, it can flood the septic system and cause overflows.
Solution: Always conduct a soil test before installation and, if necessary, modify the drain field or choose a different location.
Skipping Auckland Council Permits and Regulations
Installing a septic system without proper approvals can lead to fines, legal disputes, and forced removal of the system. Auckland Council has strict onsite wastewater system regulations to prevent environmental hazards.
Key Requirements:
- Obtain a Resource Consent if the system will discharge wastewater onto land.
- Follow AS/NZS 1547:2012 standards for septic system design.
- Ensure that the tank is installed at a safe distance from water sources.
Solution: Contact the Auckland Council early in the planning process to confirm compliance and obtain necessary permits.
Poor Placement of the Septic Tank and Drain Field
Common Placement Mistakes:
- Installing too close to wells, bores, or drinking water sources (minimum 50m distance required).
- Placing the system near driveways or heavy structures, which can lead to pipe damage from vehicle weight.
- Positioning the drain field in low-lying areas, leading to poor drainage and system failure.
Solution: Choose an elevated, well-draining area far from structures and water sources. Consult a professional for site planning.
Using the Wrong Type of Septic System
Not all septic tanks are the same. Choosing the wrong system for your property can result in poor performance and increased maintenance costs.
Types of Septic Systems:
- Gravity-fed tanks – Best for properties with natural slopes for drainage.
- Aerobic treatment units – Require power but offer advanced wastewater treatment.
- Sand filter systems – Ideal for properties with poor soil absorption.
Solution: Assess soil type, property size, and wastewater needs before choosing a system.
Incorrect Installation of Pipes and Components
The septic tank is just one part of the system—poor pipe installation can cause serious issues.
Common Pipe Mistakes:
- Pipes installed at the wrong slope (should be a steady 2% decline).
- Using low-quality or thin-walled pipes that collapse over time.
- Failure to install inspection ports for maintenance checks.
Solution: Ensure pipes are installed at the correct gradient using durable materials.
Overlooking Ventilation and Access for Maintenance
Septic tanks need proper ventilation to allow gases like methane and hydrogen sulphide to escape safely. A poorly ventilated system may cause odours in and around the home.
Additionally, some homeowners make the mistake of burying access points too deep, making it difficult to pump and maintain the system.
Solution: Ensure ventilation pipes are installed correctly and leave easy access for inspections and pumping.
Not Considering Future Expansion or Property Changes
If you plan to add more bathrooms or expand your home in the future, your septic system must accommodate increased wastewater output.
Common Expansion Mistakes:
- Installing a system too small for future household growth.
- Building patios, sheds, or driveways over the drain field, preventing access.
Solution: Plan for future expansions and ensure the system can handle additional wastewater loads.
Poor Drain Field Design and Installation
The drain field is where liquid waste is filtered back into the ground. If installed incorrectly, it can flood, clog, or contaminate groundwater.
Drain Field Mistakes:
- Using the wrong drainage materials (e.g., gravel too fine, causing compaction).
- Allowing tree roots to grow into pipes and cause blockages.
- Compacting the soil by driving heavy machinery over the field during installation.
Solution: Use appropriate gravel and drainage materials, keep trees at a safe distance, and avoid soil compaction.
Neglecting Professional Installation and Expertise
While some homeowners attempt a DIY septic tank installation, this often leads to costly mistakes and potential system failure.
Why Hire a Professional?
- Professionals ensure correct sizing, placement, and compliance with regulations.
- They avoid costly rework due to poor initial installation.
- A certified installer provides warranties and long-term support.
Solution: Always work with an Auckland-based certified septic system installer.
Closing Thoughts
Septic tank installation is a complex process that requires careful planning and adherence to local regulations. By avoiding these common mistakes—such as choosing the wrong tank size, skipping soil tests, or neglecting professional help—you can ensure your system works efficiently for years to come.
If you’re considering installing a septic tank in Auckland, consult an expert to ensure compliance and efficiency. Proper planning today will save you thousands in future repairs!
