What Is Septic Tank Design: Construction Details

What Is Septic Tank?

A Septic tank is an underwater sand basin construction utilized for dealing with the wastewater through biological decomposition and drainage procedures. It is system has a very easy structure.

It is an underground watertight compartment made of fiberglass, plastic, or concrete. The septic tank system is a simple type of onsite sewage treatment plant (OSSF) that provides only main cleaning.

Septic tanks and their helping parts are fixed underground. Usually, they are inducted at least ten feet away from the household for protection reasons. They also must be positioned far enough from springs, so users don’t risk drinking water contamination.

A tank is an outstanding form of primary sedimentation tank with a higher detention period of approx 12 to 36 hours against the duration of 2 hours in an ordinary sedimentation tank, in which digestion of settled sludge also takes place.

Septic Rank
Septic Tank

In other words, a septic tank is a joint sedimentation cum digestion tank. The septic tank has a larger capability than an ordinary primary sedimentation tank, to adjust and hold the settled sludge for its subsequent digestion.

The digestion of settled sludge is held up out of an anaerobic decomposition procedure giving growth to a septic condition, therefore this component is known as a septic tank.

Also, due to the anaerobic decomposition of the settled sludge, foul gases will be developed in the tank, and as such a septic tank will be a covered tank, It is provided with a tall vent shaft for the release of foul gases.

The sludge settled at the underside of the tank, and the oils and greasy matter increasing to the top surface of sewage as scum, are allowed to remain in the tank for 7 months, during which they are decomposed by the anaerobic bacteria to form gases and liquids by the process of sludge digestion.

The digested sludge from the tank is periodically removed approx at periods of 6 to 12 months and removed.

Read More: Septic Tank Design | Septic Tank Construction | Septic Tank Details | Septic Tank Design Example

Suitability Under the Following Condition

  • In areas where sewers have not been spread.
  • Removal of sewage from isolated communities, schools, hospitals, other public institutions, etc.
  • Soil is relatively porous and disposal of sewage by percolation into the ground is possible.

Construction Details of Septic Tank

Fig shows the details of a septic tank. The tank may be designed of brick masonry, stone masonry, or concrete.

Septic Tank Construction Details
Construction Details of Septic Tank

They are provided with a waterproof cover, along with a ventilation pipe projecting at least 2 m above the top of the building.

The tank is constructed to prevent direct currents between the tank inlet and outlet. This ensures productive sedimentation and is achieved by using tees with submerged ends as inlets and outlets.

An alternate arrangement is to provide hanging baffles in front of the inlet and before the outlet. The t-pipe or baffle at the outlet will also assist in maintaining the scum.

The floor of the tank should be of cement concrete and slope forwards to the sludge outlet. The sludge deposited and digested is removed at a duration of 6 to 12 months into a side sump well.

How Does Septic Tank Work?

A septic tank absorbs organic matter and separates suspended floatable matter like oils or grease and solids from wastewater. It is designed with two pipes which know as inlet pipe and outlet pipe.

The inlet pipe is used to transport wastewater from the house and gather it to the septic tank. It is kept here long sufficiently so that the solid and liquid waste is divided from each other.

The outlet pipe is also called the drain field or drainage station. This pipe moves out the pre-processed wastewater from the septic tank and sprinkles it evenly in the soil and watercourses.

When wastewater has been obtained after a while it will begin to, segregate into 3 layers. The topmost layer is oil or grease, and it floats above all the waste. This is commonly correlated with scum.

The middle layer includes wastewater along with waste particles. The third and bottom layer contains particles that are heavier than water and form a layer of sludge.

Bacteria inside the tank do their best to break down the solid waste, which then allows liquids to segregate and drain out effortlessly. Bacteria prepare a septic tank system work.

They break down the waste removing the water clean enough to safely percolate down into the earth. The whole is manufactured to keep bacteria healthy and busy some live in the tank, but most do work there in the drain field.

What is remain at the bottom of the tank is what needs to be occasionally removed as part of common maintenance. This is one of the explanations why a septic tank is only a basic form of sewage treatment.

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Septic Tank System

Water from the user’s kitchen, bathroom, basins, etc runs through one main drainage pipe directing to your septic tank. Underground the septic tank begins the process of carrying the wastewater. It needs to carry this long enough so the solids calm down to the bottom, while oil and grease to the top of the surface.

After this procedure, the liquid wastewater will then be eligible to exit the tank into the drain field. This wastewater is released through pipes onto permeable surfaces. These allow wastewater to filter throughout the soil.

The soil approves treats and disperses wastewater as it percolates Into the soil, finally discharging to groundwater. Finally, the wastewater percolates into the soil, naturally eliminating toxic coliform bacteria, viruses, and nutrients.

Uses of Septic Tank

Water flowing from your house is often polluted, bringing it unsafe to drink or handle. Bathing, kitchen work, and laundry work are also dirty water. Septic tanks utilize natural and mechanical processes to deal with wastewater that passes through the system.

It doesn’t matter where it eliminates undesirable solids and organic matter before returning water to the ground. That’s where your septic system comes in. septic system treats wastewater when the city sewer system is not available for use.


A well-designed and properly installed septic tank system can last for decades or fail in just a few years. It is up to users how long they use the septic tank.

Maintaining a healthful septic tank system is not all that costly but users could easily spend tens of thousands to dice up and renovate a septic tank system that has failed. Good maintenance starts with knowing how a septic tank system work and how it can fail.

A septic tank system was properly constructed and launched needing only periodic ‘pumping’ to remove the sludge from the tank. But without understanding how a septic tank works users sometimes create errors and then the system fails or is damaged.

Users need septic tanks must be pumped out regularly from time to time by pumping equipment. Pumping removes the buildup of sludge and scum, which slow down bacterial action in the tank. Regular assessment and pumping are hard so the user can check the sludge level itself with a device called the sludge judge


  • Do not require qualified supervision.
  • The sludge percentage to be removed is very less compared to that in a normal sedimentation tank. The removal in sludge volume is about 60% and the weight reduction is about 30%.
  • The cost is very small and within the reach of private householders.
  • There are no moving parts in its system.
  • The effluent can be disposed of without much trouble.
  • They are best suited for private rural areas, hospitals.
  • It can behold, etc.


  • The size required is huge and uneconomical.
  • Their functioning and action are erratic.
  • The effluent is ao dark and foul-smelling with huge biological oxygen demand.
  • The leakage of gases from the top causes a bad smell and environmental pollution.
  • Regular cleaning, removal, and disposal of sludge are often boring.

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