What is Septic Tank & Soak Pit?

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The waste water generated in the house from kitchen, bathroom as well as WC has to be disposed. If it is disposed in open it not only creates unhygienic conditions, foul odors but also invites epidemics and diseases.

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Normally in well planned cities the municipal infrastructure will have centralized sewerage network where you can connect the waste water to the municipal sewerage system. Hence if it is present there is nothing to worry.

However, when the municipal sewerage system is absent, one has to provide a septic tank and soak pit. In septic tank effluent from WC is collected. The effluent here gets treated biologically and the treated water will then be connected to the soak pit.

The waste water from the bathroom, kitchen etc. is directly connected to the soak pit. Ultimately the waste water in the soak pit will get absorbed by the surrounding soil. In a way, even if proper absorption area is available, the waste water will pollute the ground water.

Septic Tank:

The construction of septic tanks are preferred in rural areas and the fringe area of suburban and also isolated buildings and institutions, hostels, hotels, small colonies where the underground sewage system with a complete treatment of sewage may neither be feasible nor economical or simply centralized sewerage systems does not exist.

The septic tank is primarily sedimentation basin where a minor degree of solids destruction may occur due to anaerobic digestion. Septic tanks are ordinarily sized to provide a 24 hour retention time at the average daily flow from various types of residential and public buildings.

Septic Tank with portion

Septic tanks are used for wastewater with a high percentage of settleable solids, typically for effluent from domestic sources. The septic tank is a combined sedimentation cum digestion tank, where sewage is held for some period when the suspended solids settle down to the bottom. This is accompanied by anaerobic digestion of sludge that results into an appreciable reduction in the volume of sludge with release of gases like carbon dioxide, methane and hydrogen sulphide. The anaerobic action in a septic tank cannot complete the reduction of the putrefying organic matter to stable inoffensive substances. A septic tank effluent, before it has been fully oxidized is liable to become offensive when exposed to the air. The untreated effluent may cause health hazards, nuisance and mosquito breeding.

Also Read: Understand How Septic Tank and Soak Pit Work
Soak Pit

Soak Pit:

The soak pit is an ordinary pit of any shape with the least cross sectional dimension of 0.10m and 1m depth below invert level of the inlet pipe. The pit may be lined with stone, brick or concentrated blocks with dry open joints. The pit is generally filled with layer of loose stones, bricks bats and brick ballast. The pit may be covered with a RCC slab.


The Soak pit is a pit through which effluent is allowed to seep or leach in to surrounding soil. The effluent may be disposed of in a soak pit. It should be minimum 18 m and preferably 30m away from any source of drinking water, such as well, even bore well to mitigate the possibility of bacterial pollution of water supply. It should also be away from the nearest habitable building by at least 6m, to avoid damage to the structure particularly foundations.

Must Read: Frequent Problems with Septic Tank & Soak Pit.

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