Plumber’s Guide To Installing Septic Tanks

In the sprawling suburbs of Perth and the broader expanses of Western Australia, it’s not uncommon for homes to be disconnected from the central sewage system. For these homeowners, septic tanks offer a viable solution. 


However, as seasoned plumbers, Superior Plumbing can attest to the complexities involved in installing and maintaining septic systems. While DIY might be enticing to some, it’s imperative to understand the intricacies of the task at hand. 

Understanding the septic system 

The septic tank system, often perceived as a simple containment unit, is in reality a meticulously engineered solution designed to manage and treat domestic wastewater. To appreciate the nuances of this system, you need to delve deeper into its composition and functionality. 

Components and materials 

A septic tank is typically constructed from one of three primary materials: 


  • Concrete: Revered for its durability and longevity, concrete tanks can last for decades. However, they are susceptible to acidic deterioration from the sewage itself over extended periods. 


  • Fibreglass: Lightweight and resistant to rust or rot, fibreglass tanks are a popular choice for many homeowners. Yet, their lightweight nature means they can be vulnerable to shifting in unstable soil conditions or under the weight of heavy machinery passing above. 


  • Plastic: These tanks, often made from polyethylene, share many of the benefits of fibreglass, being light and resistant to rust and rot. However, their structural integrity isn’t as robust as concrete, and they may not have as long a lifespan. 


Functional dynamics of a septic tank 

The primary function of a septic tank is to provide preliminary treatment to domestic wastewater. Here’s a breakdown of the process: 


  • Inlet and outlet pipes: Wastewater enters the tank through an inlet pipe, settled at one end, and exits through an outlet pipe on the opposite end. The positioning ensures that the flow is streamlined and doesn’t disturb the sedimentation process. 


  • Sedimentation and separation: As wastewater remains in the tank, a separation process ensues: 
  • Scum layer: Lighter waste materials, like oils and fats, rise to the surface, forming a layer called ‘scum’. 
  • Sludge layer: Heavier solids settle at the bottom, resulting in the formation of the ‘sludge’ layer. 
  • Effluent: The relatively clear water sandwiched between the scum and sludge layers is termed ‘effluent’. This is the portion of the wastewater that proceeds to the next stage of the treatment process. 


  • Anaerobic digestion: Within the tank, anaerobic (without oxygen) bacterial action breaks down the solids, reducing their volume and converting some of the materials into gases, such as methane and carbon dioxide. 


  • Effluent transfer to drainfield: The clarified effluent flows from the tank into the drainfield, also known as a leach field or seepage field. Here, further treatment occurs as the effluent filters through the soil, benefiting from aerobic bacterial action before eventually joining the groundwater. 

Maintenance aspects 

For the septic system to function optimally, it will require: 


  • Regular pumping: The scum and sludge layers can’t be broken down entirely by bacterial action. As such, over time, they accumulate and can take up a substantial portion of the tank. Regular pumping (typically every 3–5 years, depending on usage) removes these build-ups. 


  • Inspection: It’s advisable to have a professional such as Superior Plumbing inspect the system every 1–3 years to ensure its components are in good condition and to assess when pumping is needed. 


  • Mindful usage: Homeowners should avoid disposing of non-biodegradable items, harsh chemicals, and excessive fats/oils down the drain, as these can disrupt the bacterial ecosystem and clog the system. 


The step-by-step process of installing a septic tank 

The process of installing a septic tank is intricate, spanning from initial site assessments to post-installation landscaping. Each step is crucial for ensuring efficiency and environmental safety. This guide breaks down the essentials for a streamlined and effective installation. 

Preliminary site assessment and percolation test 

Preliminary site assessment: This involves evaluating the proposed septic location, considering topography, nearby water bodies, vegetation, and other obstacles. The goal is to ensure environmental safety and system efficiency. 


Percolation test: The ‘perc test’ gauges the soil’s absorption ability, influencing the drainfield’s design and size. It’s essential for system efficiency and groundwater protection. The process of this test is as follows: 


  • Hole preparation: Holes are bored in the proposed drainfield area, usually around 12 to 18 inches deep. 
  • Water filling: Holes are filled to simulate standard conditions and let the soil presoak, ensuring measurement accuracy. 
  • Measurement: The water level’s decrease is monitored at regular intervals to understand the soil’s absorption rate. 
  • Result analysis: The drop rate helps calculate the soil’s percolation rate, indicating soil type and guiding septic system design. 

Design considerations of the septic tank 

Size of the household: The number of people residing in the home directly influences the amount of wastewater generated. A larger family will require a more robust system to handle the increased wastewater volume. 


Land area: The available space for the septic system determines the extent to which the system can be spread out. This influences both the size and shape of the drainfield as well as potential placements for the septic tank itself. 


Soil absorption capacity: As gauged by the percolation test, the soil’s capacity to absorb and treat wastewater is a pivotal factor. Soils with high absorption rates may need differently designed drain fields compared to those with lower rates. 

Design outcome 

The culmination of these considerations is a comprehensive blueprint tailored to the property’s unique requirements. This blueprint includes: 


  • Tank size: Based on the household’s wastewater generation, the blueprint will specify an appropriately sized tank to ensure efficient treatment and prevent overflows. 


  • Tank type: The material (concrete, fibreglass, or plastic) and design of the tank will be chosen based on longevity, strength, and suitability to the specific site conditions. 


  • Piping layout: Detailed schematics will illustrate the path and gradient of inlet and outlet pipes, ensuring smooth wastewater flow and accessibility for maintenance. 


  • Drainfield design: Depending on the soil type and absorption rate, the blueprint will outline the drainfield’s size, shape, and depth, optimised for efficient water treatment and dispersal. 

Securing the necessary permits 

Local councils, especially in Perth, have stringent rules around septic systems to protect both the environment and public health. Always consult with the Perth regulatory bodies to ensure full compliance. Superior Plumbing, Drainage and Gas can take care of all this for homeowners meaning they don’t need to spend time learning which permits they require and how to go about getting them. 


Heavy machinery, often an excavator or a backhoe, is needed. The hole’s depth and size depend on the septic system’s design, but it must accommodate the tank and have room for workers to manoeuvre. 

Installation of the tank 

The tank is carefully lowered into the excavated hole. Ensuring the tank remains level is crucial to its proper functioning. 

Connecting the plumbing system 

Precision is crucial in septic system installation. The gradient of pipes must be optimised to ensure consistent wastewater flow and prevent sediment buildup, which can cause blockages. Equally vital are the connections between pipes; they need to be tightly sealed to avert leakages, which can result in environmental hazards, odours, and system malfunctions. Proper installation directly impacts the system’s efficiency and lifespan. 

Laying out the drainfield 

A series of trenches, often filled with a specific grade of gravel, allows the treated wastewater to percolate into the ground. The length, depth, and width of these trenches depend on the percolation test results. 

Backfilling and landscaping 

After installation, the area around the system is backfilled with soil. This backfilling is not just a mere cover-up; proper grading is crucial. Proper grading ensures water doesn’t pool atop the site, and it’s vital to channel rainwater away from the drainfield, safeguarding the system’s efficiency and longevity. 

Advantages of hiring professionals like Superior Plumbing 


  • Knowledge and skill: The installation of a septic system is not just about manual labour; it requires a deep understanding of plumbing systems, soil science, and local regulations. 


  • Specialised equipment: Superior Plumbing have access to machinery and tools that make the process efficient and ensure longevity. 


  • Troubleshooting: Professionals can foresee potential problems with the installation, something a DIY approach might miss. 


  • Savings in the long run: Mistakes in septic tank installation can lead to expensive repairs or even a complete overhaul down the road. 


  • Warranty and peace of mind: Knowing that the installation is backed by a warranty can be reassuring. It’s a testament to the quality of the work done. 

Final thoughts 

Installing a septic system is a complicated task, with implications not just for homeowners but also for the environment. Especially in regions like Perth, where local regulations are stringent, the margin for error is minimal. Superior Plumbing, with its vast expertise and access to specialised equipment, ensures that the installation is efficient, compliant, and cost effective. 


While DIY might seem appealing, the potential risks and future costs associated with mistakes can be significant. The value of entrusting this task to professionals, who bring with them years of experience, can’t be overstated. In sum, when it comes to the critical infrastructure of your home, it’s best to rely on experts. For peace of mind, longevity, and optimal performance, choose Superior Plumbing, Drainage and Gas for your septic tank installation. Get in touch today for a consultation and ensure your septic needs are met professionally.