How a SEPTIC TANK works and How to build a septic tank step by step
In this post, I clearly show you exactly how a septic tank works and how to build a septic tank system. You will also learn how to build its soak away.
How Septic Tank Works and How to Build One: A Step-by-Step Guide
Table of Contents
Core Concept or Idea
What is a Septic Tank?
Difference Between Sewage and Waste Water
How Does a Septic Tank Work?
Materials Needed for Building a Septic Tank
Step-by-Step Guide to Building a Septic Tank
6.1 Step 1: Excavation
6.2 Step 2: Cast Concrete Bed
6.3 Step 3: Construct the Walls
6.4 Step 4: Plumbing Installation
6.5 Step 5: Shuttering for the Top Slab
6.6 Step 6: Fill the Soak Pit
Maintenance and Care for Your Septic Tank
Conclusion
FAQs
Core Concept or Idea
In this post, I’m going to share with you an easy step-by-step guide on how you can build a simple septic tank with its soak pit.
As a civil engineer with years of experience in building and construction, the method that I’m about to show you on how to build a septic tank is better because the septic tank can be repaired easily. It has low operating costs and low capital costs.
This method is a simpler way to build a septic tank that can literally be understood by everyone on the face of this planet.
In this guide, you will learn how septic tanks function and provide a detailed step-by-step method for constructing one. By the end of this post, you will have the knowledge to build a septic tank using locally available materials, making it a cost-effective solution for waste management.
What is a Septic Tank?
A septic tank is an essential component of a plumbing system designed to manage sewage and waste water. It collects sewage from various sources in the home, such as toilets, sinks, bathtubs, and washing machines. Once the sewage (faeces and urine) enters the septic tank, it undergoes a natural purification process that ultimately returns treated water back to the groundwater system.
Difference between sewage and waste water
Let’s first clearly understand these two terms before proceeding.
Sewage, in simple terms, is faeces and urine, whereas waste water is water from bathrooms, bathtubs, water from the sink, and any other water with fats and soap.
How does a septic tank work?
The tank operates by separating solid waste from liquid waste. Solid sewage settles at the bottom of the tank, whereas the liquid sewage flows into a soak pit or leach field, where it is further treated by the soil.
Understanding this process is fundamental for anyone looking to build a septic tank.
The functioning of a septic tank involves a series of steps that ensure sewage and waste water are properly treated before they re-enter the environment. Here’s a breakdown of how the system works:
Inlet Pipe: Sewage from the house enters the septic tank through an inlet pipe.
Separation of Waste: Inside the tank, solid waste settles at the bottom of the first chamber, forming sludge, while lighter materials like grease float to the top, forming scum.
Bacterial Action: Bacteria in the tank break down solid waste into liquid form which then moves to the second chamber, a crucial step in the treatment process.
Outlet Pipe. Liquid sewage from the second chamber flows to the soak pit or leach field through the outlet pipe
Flow to Soak Pit: Once the liquid sewage reaches a certain level, it flows into the soak pit or leach field, where it is filtered through soil, further purifying the water.
The process continues like that every time you use your toilet.
It’s important to manage what goes into the septic system. Items like baby wipes, feminine products, oils, and grease can disrupt the bacterial process and lead to system failures or blockages.
Materials Needed for Building a Septic Tank
Before starting the construction of a septic tank, gather the necessary materials. Here’s a list of what you will need:
Bricks or blocks
PVC pipes and fittings
HDPE pipes
Sand and cement
Aggregates
Timber for shuttering
Steel iron bars
Hardcore for the soak pit
Waterproofing powder or liquid
Step-by-Step Guide to Building a Septic Tank
Now that you have the materials ready, let’s walk through the steps to build a septic tank. Following these steps will help ensure that your septic system is effective and durable.
Step 1: Excavation
The first step is to excavate the area where the septic tank and soak pit will be placed. Before excavating,
Understand the necessary dimensions:
The size of the Septic Tank
The size of the soak pit
The minimum distance from the main building
Dimensions vary based on the number of users.
Table showing the minimum septic tank sizes for different number of users
The table below shows the minimum recommended size for the soak pit
The table below shows the minimum distance of the septic tank to different elements
Step 2: Cast Concrete Bed
After excavation, the next step is to cast a concrete bed at the bottom of the pit. Use a concrete mix of grade 15 with a ratio of 1:3:6 (one part cement, three parts sand, and six parts aggregates). The depth should range from 100mm to 200mm.
Step 3: Construct the Walls
Once the concrete bed is set, it’s time to build the walls of the septic tank. You can use concrete blocks or clay bricks with a wall thickness of at least 200 millimeters. The first chamber should occupy two-thirds of the total length, while the second chamber takes up one-third. For example, if the total length is 3 meters, the first chamber will be 2 meters, and the second chamber will be 1 meter.
At this stage, you can do plastering or do it at a later stage. You have to plaster the walls while adding water-proofing powder to the sand, so the mix will include sand, cement, and water-proofing powder, all mixed with water to the required workability for plastering.
Building walls without pillars or columns is a big mistake.
Step 4: Plumbing Installation
Plumbing is the most important and crucial part that has to be taken. And plumbing a septic tank is so simple you have to simply follow this concept.
All sewage, i.e., faeces and urine, has to be directed towards the septic tank.
All waste water, i.e., water from the sink, bathroom, bath tab, all water with fats and soap, or any other water from the house, should be directed towards the soak pit without passing through the septic tank chambers. Simply tell your plumber to do that.
This is simply because soap and fats will disrupt the process bacteria in the septic tank, changing solid sewage to liquid sewage that can easily soak away into the ground.
When you plumb it this way, the septic tank can last over 30 years without pumping, and then when you direct waste water into the septic tank chambers, you will need to pump every 2–5 years depending on the usage.
The plumbing installation is crucial for the system’s functionality. Fit the inlet and outlet pipes, ensuring that the inlet pipe is positioned higher than the outlet pipe. This design allows for easier flow of liquid sewage from the second chamber to the soak pit. After plumbing, plaster the walls and apply waterproofing materials to protect the tank.
Step 5: Shuttering and steel reinforcement for the Top Slab
Shuttering is necessary to prepare for the concrete top slab; it must be a solid slab. A solid slab in simple terms is one entirely made of steel bars and concrete with no hollow chores running through it. Use timber for shuttering and steel bars for reinforcement. The steel bars should be spaced 200 micrometres apart. For the top slab, consider using concrete of grade 20 or 25; use a mix ratio of 1:2:4 (one part cement, two parts sand, and four parts aggregates). Once the concrete has dried, plaster top the exterior of the septic tank and install the manholes.
The way you decide the position of a manhole is also simple; you have to position them at points or intervals in a way that, in case of any blockage, you are able to use a loading stick and push inside the pipe to allow the easy flow of the sewage.
Step 6: Fill the Soak Pit
The final step is to fill the soak pit with hardcore material. This step is essential for ensuring proper drainage and functionality of the soak pit.
Maintenance and Care for Your Septic Tank
Building a septic tank is just the beginning. Regular maintenance is key to ensuring its longevity and effectiveness. Here are some tips for maintaining your septic system:
Regular Inspections: Have your septic system inspected regularly to identify any potential issues early.
Pumping: Schedule pumping of the septic tank every 3-5 years where necessary, depending on usage.
Watch What You Flush: Avoid flushing non-biodegradable items that can clog the system.
Use Bacteria Additives: Occasionally, adding bacteria can help maintain the breakdown of solids.
Conclusion
After building the septic tank, fill it with water to full capacity before use.
Building a septic tank may seem like a difficult task, but by following these steps, you can create an efficient waste management system for your home.
Understanding how a septic tank works and maintaining it properly will ensure that your system functions effectively for many years to come. Also note that with the right knowledge and materials, you can confidently complete this project and contribute to a more sustainable environment.
Frequently Asked Questions
How often should a septic tank be pumped?
Generally, a septic tank needs pumping depending on the usage and the plumbing style.
When both waste water and sewage are directed towards the septic tank, you will need to pump every 3-5 years.
On the other hand, when plumbing and only sewage are directed to the septic tank, then waste water is directed to either the soak pit or public sewer, and your septic tank may last even up to 20 years without the need for pumping.
For example, the septic tank for the house where I grew up at home was built long before I was born and has never been pumped. My parents told me the septic tank was built in 1990 and also told me that the soak pit was extremely big.
All waste water was directed towards the soak pit without passing through the two compartments of the septic tank, then only sewage (faeces and urine) was directed towards the septic tank to be broken down into liquid sewage, which later also flows to the soak pit to be drained to the underground.
What can I do to maintain my septic tank?
Avoid flushing non-biodegradable items, such as baby wipes and female pads, into the toilet.
Be mindful of what you flush into your toilet. No oils, fats, grease, or chemicals, as these will hinder the process of breaking down solid sewage to liquid sewage.
It is recommended to excavate an extremely large soak pit because the functioning of the septic tank is entirely dependent on the rate at which the soak pit is able to soak away the liquid sewage. A small soak pit will make you regret it sooner as it fills up so fast and it can no longer drain the liquid sewage to the underground.
Use water efficiently when flushing waste water and sewage to avoid overloading the system.
You also have to install a trap in your plumbing system.
Use either the P-trap or an S-strap. The main function of the trap is to keep bad odours or smells from escaping from the system.
They also serve another function of trapping small objects that might fall in the toilet bowl. It’s important to hire a professional plumber to help you choose from the two depending on the requirements for your house.
What should I avoid flushing into a septic tank?
Fats, oils, and grease
Chemicals such as pesticides, bleach, or any other laboratory chemical
Non-biodegradable items such as nappies or pampers, feminine products such as pads, or any other feminine hygienic products
How long does a septic tank last?
A septic tank can last 20–40 years or even longer.
How much does it cost to pump a septic tank?
The price for pumping a septic tank ranges between 150 and 400 USD, depending on the size of your septic tank and your local pricing. For example, the price for pumping septic tanks here in my country is generally around 150 USD.
What is a soak pit or soak way?
This is a component of a septic tank system that serves the primary purpose of soaking away liquid sewage into the soil underground for further treatment.
What can damage my septic tank?
Flushing harmful chemicals that disrupt the bacterial process of turning solid sewage into liquid sewage
Driving or parking heavy equipment over the tank or soak pit or leach field as it would dismantle the top slab of the septic tank
I also created a video on how to build a septic tank from start to finish, you can check it our YouTube channel here