How to Install a PVC or Plastic Septic Tank-Step-by Step Guide

How to install a plastic septic tank-step-by step guide

Table of contents

1. Core Concept or Idea

2. Why is using a plastic septic tank better?

3. What is a septic tank?

4. How does a septic tank work?

5. Steps to install a plastic septic tank into the ground

Step 1: site clearance and excavation

Step 2: Place the plastic septic tank inside the pit. Step 3. Filling the tank with water

Step 4: Backfilling

Step 5: excavate the pit and soak the pit

Step 6 is plumbing.

6. Frequently Asked Questions

Core Concept or Idea

In this post, I’m going to share with you a simple step-by-step guide on how you can install a simple plastic septic tank with its soak pit. The method that I use in this post is better because it is experience-based, tested, and trusted, and you can rely on it if you are looking forward to undertaking this kind of project.

As a civil engineer with years of experience in building and construction, I’m going to show you a technique that is simple and easy to apply.

You use low operating costs and low capital costs, and by the end of this post, you will have known how to install this plastic septic tank by yourself from start to finish, so be sure to read this post till the end.

Why is using a plastic septic tank better?

This plastic septic tank is better because it is easy to install.

It is cheaper compared to concrete tanks and also can be used in very hilly areas where concrete septic tanks are impossible to build.

You can also use these plastic septic tanks in waterlogged areas.

What is a septic tank?

A septic tank system is a crucial component that is part of a plumbing system that takes waste water and sewage from your house and purifies it back into the groundwater system.

Therefore, waste water from the bathtub, sink, bathroom, and showers will be directed towards the soak pit, and also sewage from toilets ends up in the ground with the help of the septic tank system.

How does a plastic septic tank work?

This is how the septic tank works

Sewage comes from the house through the inlet pipe to the first chamber; solid sewage remains at the bottom, then liquid sewage goes to the second chamber.

Bacteria grow naturally from the first chamber, breaking down the solid sewage to make it liquid sewage. The liquid sewage then flows to the second chamber.

When it reaches this level, it flows to the soak pit.

The liquid sewage will then flow through the hard core to the underground. It’s a continuous process every time you use your toilet.

The first chamber is usually 2/3 then the second chamber as 1/3. That is the thumb rule for determining the length of the first chamber and second chamber for all septic tanks with two chambers.

If the total length of the tank is 6 m, the first chamber is 4 m, and then the second chamber is 2 m.

Steps to install a plastic septic tank into the ground

Step 1: site clearance and excavation

Do site clearance and remove top soil not exceeding 300 mm and dispose away from the site

Set out and excavate the pit where to place the septic tank based on its dimensions.

While excavating, you don’t have to add any allowance in the sides; you have to excavate exactly the dimension for the plastic septic tank so that when placing it, it can fit exactly and perfectly without leaving any gaps in the sides.

This is to prevent floating of the tank in case water goes below the bottom of the tank. It remains intact.

Secondly, when excavating, excavate the exact depth while keeping in mind the level of the finished outside ground level.

The top level of the septic tank has to be slightly lower than the ground level. So when excavating, let’s say the height of the tank is 1.7 m. When excavating, add an extra 300 mm to make the total depth 2 m.

After backfilling, we can build a brick manhole around each of these 2 covers. The 2 brick manholes will be the ones matching the level of the ground, which we shall later provide with concrete manhole covers.

If the area where you are placing the tank is too waterlogged, first lay a hard core in the pit not exceeding 200 mm thick and do sand blinding before placing the tank.

Step 2: Place the plastic septic tank inside the pit.

To safely put the tank inside the pit, tie a rope around the tank and then use a pulley to effortlessly place it safely without damaging it. The common mistake people make here is trying to lift it with hands; it’s quite heavy, and it might slip up from the hands and break since it's plastic.

Step 3. Filling the tank with water

After placing the tank in the pit, immediately fill it with water. You can use a water pump or any other means to fill the tank to full capacity to prevent folding at the time of backfilling, and that’s why it’s so crucial to immediately fill the septic tank with water as soon as you place it in the pit and then cover the tank properly with its covers.

Step 4: Backfilling

After filling the tank with water, backfill with imported marrum. Don’t use marrum with stones because it might damage the tank.

Start by backfilling at the four corners to avoid folding, and then you can backfill the middle part later.

Step 5: Excavate the for the soak the pit and fill it with hardcore

Excavate the pit for the soak pit depending on the number of users. It is advisable to excavate a bigger soak pit above the number of users; for example, if you have 20 users for your septic tank, excavate a soak pit for 30 users. This is because the plastic septic tank entry depends on the rate at which the soak pit is able to soak away the liquid sewage. That’s why a bigger soak pit is required.

Step 6 is plumbing.

This is the most important step among all these other steps. For the longevity of the septic tank, the trick is so simple. Simply do the plumbing pipe work in a way that all waste water, that is, water from the sink, the bathroom, and all water from cleaning the house, should be directed to the soak pit or to a public sewer, roadside drain, or ditch.

Then, on the other hand, sewage from the toilet and urinals should be directed towards the septic tank. The concept for plumbing for a septic tank is as simple as that.

Waste water should not go through the septic tank. This is because it contains fats and soap, which hinder the biological decomposition of the sewage.

Also build manholes at necessary positions. Plumbing has to be done in a way that you create a manhole in positions where it will be easy to use a loading stick to unclog any part of the system that might be affected in the future. The concept of locating manholes is as simple as that.

The major materials that we use when doing pipework are PVC cement, 100mm dia pies, pipe bends, Ts, and other plumbing fittings.

Insert a T at the end of the inlet pipe and also a T at the outlet pipe inside the septic tank.

Lastly, build a brick manhole with a precast concrete manhole cover around the 2 covers to protect the manhole from any damage.

Frequently Asked Questions

What is a plastic septic tank?

A plastic septic tank is a light-weight, durable tank used to dispose of sewage and waste water from houses and then purify it back into the groundwater system.

How deep should a plastic septic tank be buried?

A plastic septic tank should be buried depending on its height. For example, if the plastic septic tank is 1.5 m, simply add 300 mm and excavate a pit that is 1.8 m, meaning you will have buried the tank at a total height of 1.8 m.

How long does it take to install a plastic septic tank?

It usually takes 1-3 days to install a plastic septic tank, including the time for excavating the pit. This period depends on the nature of the soil.

What is the cost for purchasing a plastic septic tank?

The cost of purchasing a plastic septic tank ranges from 500 USD to 2000 USD depending on the size and the local prices in your country. For example, we bought this 5000 L plastic septic tank at 670 USD, and the labour cost for installing it was just 100 USD.

How much does it cost to install a plastic septic tank?

The labour cost for installing a septic tank ranges from 100 to 200 USD, depending on the size and location where it is being installed.

How long does a plastic septic tank last?

With a big soak pit able to fully soak up the liquid sewage from the septic tank, a plastic septic tank can even last up to 20-30 years.

Do plastic tanks require ventilation?

Yes, plastic septic tanks require ventilation to prevent pressure buildup inside the tank. The way we do ventilation is simple; we do it within the plumbing system. We can provide a vent pipe with a fly trap usually at the external side of the wall where the the septic tank joins the main house

How do I prevent a plastic septic tank from floating?

After placing the septic tank in the pit, backfill the 300mm on top and build 2 brick manholes with necessary concrete manhole covers on each of the 2 openings of the plastic septic tank. This way the plastic septic will never float because it has the 300mm marrum backfill on top and also the 2 brick manhole.