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What is Septic Tank? | Septic Tank Size and Dimensions

What is Septic Tank? | Septic Tank Size and Dimensions

Septic Tank Meaning:

A Septic tank is an underground tank for receiving waste matter to be putrefied and decomposed through anaerobic bacteria.

A septic tank consists of one or further concrete or plastic tanks of between 4000 and 7500 liters. one end is connected to an inlet wastewater pipe and the other to a septic drain field. Generally, these pipe connections are made with a T pipe, allowing liquid to enter and exit without disturbing any crust on the surface. Today, the design of the tank generally incorporates two chambers, each equipped with an access opening and cover, and separated by a dividing wall with openings located about midway between the bottom and roof of the tank.

How does a Septic Tank Work?

  • Anything that goes down the toilets in your home ends up in your septic system.

Waste gets segregated into 3 layers

1. Scum                       2. Liquid              3. Sludge

  • Microbes naturally present in the tank start degrading the sludge by eating it up.
  • The excess water goes to the second compartment through the baffle.
  • further treatment takes place by the MICROBES in the second compartment.
  • the excess treated water gets discharged through the pipes in the soil.
  • nature has provided a microbial mechanism to treated sewage in a septic tank.

But this mechanism gets disrupted due to various reasons:

  1. due to heavy usage of water
  2. slow sludge breakdown due to heavy usage of chemical cleaners

Septic Tank Failure:

That can lead to further problems like

  • overflow contaminating the ground water
  • backflow

We can avoid these failures by maintaining the septic tank without any hassles.


Septic Tank Size and Dimensions:

1. Minimum size of septic tank:

Septic tank design ( size & capacity )
IS code – 2470 – 1963 part 1
Person capacity length (L) breadth (w) height (D)
4 2000 1.8 0.9 1.55
6 2250 2 0.9 1.55
8 2800 2.25 1 1.55
10 3500 2.5 1 1.7
14 5000 3 1.2 1.7
25 10000 4 2.4 2.4
  • The minimum Width of the septic tank is 2.5 feet or 750mm.
  • The length of the septic tank is 3 to 4 times than width.
  • Depth is not less than 1 meter or 3.28 feet.

Note: This septic tank size is enough for 4 to 6 family members.

2. Septic tank Wall Thickness:

If a septic tank is made up of brick work then,

  • Outer wall thickness – 9″ or 228mm
  • Inner wall thickness –  4″ or 100mm

If a septic tank is made up of RCC then,

  • All walls outer wall and inner wall not less than 6″ or 150mm

3. Septic tank must have 3 partition chambers.

  • 2 partition septic tank is not preferred in the septic tank.
  • Man hole diameter not less than 2 feet for easy maintenance.

Important Points About Septic Tank:

  • Use only first-class bricks in construction and dip in water properly before use.
  • mortar ratio 1:3 or 1:4.
  • mortar ratio for plaster 1:4 or 1:5, Plaster thickness 18-20mm.
  • The best place for a septic tank is under stairs or pouch area otherwise in the parking area. not construct in your room and kitchen because maintenance is required after year and it is difficult to clean if it is in room or kitchen.
  • Free board distance in a septic tank is not less than 1 feet.
  • minimum diameter of the pipe ( inlet & outlet ) not less than 4″ or 100mm and minimum diameter of the vent pipe is 2″ or 50mm.
  • maintain a distance between the house wall and the septic tank.
  • maintain septic tank slope 1 in 30.
  • maintain a proper distance in the septic tank and borewell according to the public health department minimum distance is 50 feet but practically if it is not possible then provide min. 10 feet distance.
  • A septic tank should be minimum 1-2 feet far from the house wall.

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