When is a septic tank better than a pit?


A private house is comfort and coziness (to the extent that you yourself provided), as well as freedom from careless neighbors, irresponsible ZhEKs, but also responsibility for maintenance.

If you have already brought water to the house, then it’s time to get an autonomous sewer.

However, before giving preference to a cheap and “angry” option, we recommend that you think about it for a minute and calculate for the future. And she, over time, will present the following requirements.

The tightness of the structure. This question is relegated to the background by many, but in vain, because depressurization is fraught with the release of waste products into open ground and getting into groundwater (knowing this, will you drink water from your well without fear?).

Longevity of the structure. The timing of the next repair and whether it will be needed at all will depend on the quality of the material and the work performed.

Effluent recovery from the storage capacity, the question is vital. You should decide where to put it all and how often to do it.


In order to make an objective assessment of known sewer systems, we will discard the material aspects of their immediate arrangement and turn to issues of subsequent operation.


Perhaps this is a great option. And if you have such an opportunity, be sure to use it. The cost of construction and the complexity of installation (electricity is required) make this design more attractive for collective use (connect several houses, but the question of whose territory to install can stall the whole thing).

In general, for a small house or cottage, this sewage treatment system is not very suitable because of the high cost.


The complete opposite of the previous version. This is a fairly traditional and popular type of autonomous sewage for a private house. The thing is that it is good only where the daily use of the benefits of civilization entails a minimal (or very economical) amount of liquid waste, and therefore, calling an assinizer will result in an acceptable amount for you.

The volume of the assinizer is 4 m3. This means that the volume of the cesspool should be planned so that the useful volume (bottom area multiplied by the height from the bottom to the drain pipe) is close to 3.5 m3.

It is worth mentioning the indescribable «feelings» during and after cleaning the pit, which will be present on your site for about a day every 1-2 months.


At this time interval, this is a more civilized way of discharging and treating domestic wastewater than a cesspool and less costly and autonomous than a deep cleaning station.


The essence of the method is to divide the container for collecting liquid waste into chambers. Schematically, the whole system looks like this.

The first chamber collects effluents, primary decomposition and settling to the bottom of heavy fractions take place in it.

Partially clarified liquid (50-60%) flows through the hole in the upper half of the wall into the second chamber. Here the process of decomposition and settling of solid particles continues.

Effluents clarified up to 35% are discharged to the filtration system, where they are further treated and discharged into the ground.

All biological processes proceed naturally, and only in the filtering structure it is recommended to use biological preparations that accelerate the process of sediment decomposition.

As you can see, the system includes, in fact, a septic tank, as a reservoir for collecting and settling waste, and a filtering facility for draining waste into the ground in a decontaminated form.

The best option is to use ready-made containers made of polypropylene with a wall thickness of at least 7mm.

It is possible to make a two-chamber septic tank made of reinforced concrete or reinforced concrete ringsbut in this case it is necessary to ensure the tightness of the structure during operation.


About 200 liters of water are consumed per person daily, approximately the same amount is poured into the sewer.

The volume of the septic tank is equal to the three-day total water consumption of all the inhabitants of the house. That is, for a family of 4 people, it will be 4 x 200 x 3 = 1400 liters. In total, you will need a container with a total volume of 1.5 m3.

But, as we have already found out, the system consists of several cameras. The number of chambers depends on the total volume of wastewater per day.

If it is less than 10m3, then two cameras are enough, if more, then three cameras are made. Each chamber is either a separate compartment with an overflow in the upper part, or a separate container.

At two-chamber division prescribe the following proportions: the first — at least 75% of the total volume.

Three-chamber division assumes the following ratio (first:second:third): 50%:25%:25%.

In our case, for a family of 4 people, the first chamber is 1.1 m3, the second is 0.4 m3. If these are separate containers, then you should round up to standard sizes and choose one per 1 m3and the second at 0.5 m3 (if you want to play it safe — choose the same 1 m3).

Location selection for a septic tank must meet the following requirements:

  • no closer than 5 m from the house,
  • free access of the assistant to the hatch must be provided.


The septic tank itself is not a treatment plant and, from the point of view of ecology and sanitary standards, must be supplemented with a filter structure. If we take into account the small area of ​​\u200b\u200bthe plots of our compatriots, then the most acceptable from all points of view are the factory design of the post-treatment or the filter well.

Their principle of operation is simple: water enters the filter tank, located on a sand and gravel cushion, and passing through the drainage is subjected to natural cleaning.

What is good factory design:

  • a lightweight and at the same time durable polypropylene body is buried in the ground and does not manifest itself in any way (in the form of hatches);
  • the water goes down because the structure of the hull prevents the upward movement, so it is safe to grow garden crops in this area.

Some disadvantage of this option is the gradual silting of the filter layer and after 7-10 years it should be updated. To facilitate the process, each drainage layer is laid on geotextiles, which will significantly delay the renewal period and facilitate the process of changing drainage.

Perhaps the best option would be well from reinforced concrete rings. Its advantages: access to the content — you can use the method of biological treatment. 1 package of bioadditives per year — and you will forget about replacing the drainage layer.

To build a well, they dig a hole three rings deep plus 30 cm into the drainage layer. The diameter of the pit exceeds the diameter of the rings by 50 cm.

As you already understood, the design will consist of 3 rings, the lower of which is perforated with holes with a diameter of 40-60 mm. The total area of ​​the holes must be at least 10% of the area of ​​the walls of the entire well.

The bottom and walls of the pit are lined with geotextiles, a crushed stone-sand cushion 30 cm thick is laid on it and a sieve ring is erected. The sides are sprinkled with the same drainage mixture below the upper level of the ring.

The following rings are alternately installed on top of each other with a cement mortar with a penetron (or its analogue) interconnected. The sides are also sprinkled with rubble. Slightly above the level of the supply pipe, the geotextile is fixed with a strapping around the well, and further backfilling is carried out with soil. The structure is closed with a concrete tablet (put on a solution) with a hole for the hatch.

CONCLUSION: if you use polypropylene containers of sufficient thickness (7 mm) and build a drainage well with subsequent biological treatment, then you will create a very durable (at least 50 years) sewerage system with an annual maintenance cost equal to the cost of a single call to an assinizer plus a biological treatment package.


  • groundwater level above 2.5 m (will pop up as in the photo on the right);
  • within a radius of 25 m there is a well or well (your or neighbors);
  • the distance to the residential facility is less than 5 m;
  • the site is located on clay soils (here the question is moot: there are no obstacles for concrete on any soil, and a sealed container on clay can be pushed out, but it can be anchored).

POSITIVE SIDES septic tank applications:

  • ease of maintenance (removal of silt from the first compartment is carried out 1-2 times a year);
  • does not consume electricity, and, therefore, non-volatile;
  • independent of the ambient temperature, in winter it works the same way as in summer;
  • allows long interruptions in the operation of the system.

To begin with, let’s look at a solution for draining sewer water from a house that is common to all structures.

INTERNAL PLOT sewerage system runs through the territory of the house. Drains from all plumbing fixtures, machines (washing machines and dishwashers) are discharged into the external sewer through a vertical riser located inside the house.

For laying this part of the sewer, plastic pipes are used, interconnected by means of fittings (standard connectors). This is a fairly economical and reliable version of the domestic wastewater disposal system.

The common riser is led outside the house through a hole in the foundation. Its standard size is 300×300 mm. Naturally, it significantly exceeds the dimensions of the outlet pipe, but it should be noted that over time the foundation may shrink, and the gap will ensure the integrity of the sewer pipe.

BATHROOM and WASHING connected to the riser with pipes with a diameter of 50 mm through a water seal (siphon), which will prevent unpleasant odors from entering the dwelling.

Pipes lead to the riser at a slope, which prevents them from clogging. The slope should not exceed 25 mm per 1 m.

WASHING and DISHWASHING machines do not need a water seal. Waste soapy water drains directly to the nearest sewer pipe.

TOILET already contains a water seal in its design, and therefore a pipe with a diameter of 100 mm is directly connected to it.

OUTSIDE PLOT represented by a collection of pipes coming out of the house and outbuildings. Its task is to connect the sewer system of the house (outbuildings) with a container for collecting and settling domestic wastewater.

Here it is also necessary to observe slope 20 mm per 1 m of pipe. Calculate the length of the pipe from the house to the sump, multiply by the amount of slope and take this value into account when you dig a trench from the house to the sump.

Minimum bookmark depth external sewage pipes is 0.7 m for the southern regions and 1.8 m for the northern latitudes. This is according to the standard. If for some reason this depth cannot be observed, then all outgoing pipes are carefully insulated.

Pipes are laid on a sand cushion, sprinkled with sand from the sides and top, after which they are covered with soil.

When it is not possible to lay a straight section, in places of bends the lines are equipped manholes from brick or reinforced concrete rings with mandatory external waterproofing.

If for the external area are used plastic pipes, they are interconnected by means of a rubber ring located in the socket.


Dig under a septic tank foundation pit taking into account the linear dimensions of the container:

  • width and length should be 50 cm more than the same parameters of the tank;
  • depth calculated taking into account the depth of the incoming pipe of the external sewer, add another 20 cm to this size (the thickness of the concrete pad on which the treatment plant is installed.

The bottom of the pit is carefully rammed, and then two installation options follow:

  • 20 cm sprinkled with a dry sand-cement mixture (proportion: 5 parts of sand to 1 part of cement),
  • a 20 cm concrete pillow is poured, ears are mounted in it (two on each side to fix the container.

A septic tank is installed on the base.

Under reinforced concrete containers, a gravel-sand cushion is sufficient.

Connect the inlet and outlet pipes. If their depth of occurrence is less than that set out in the section WITHDRAWAL OF WASTE FROM THE HOUSE (outer area), then the pipes must be wrapped with rolled thermal insulation to a thickness that compensates for the depth of soil freezing.

For example, one layer of insulation 10 mm replaces 25-40 cm of soil. Count the number of layers based on your bookmark depth.

A polypropylene septic tank must be “anchored” to prevent it from “floating”. On both sides, chains are thrown through it and attached either to ears poured into concrete, or 10 mm of reinforcement at least 1 m long are threaded through the extreme links.

Next, the container is gradually filled with water and at the same time sprinkled with sand (when mounted on a slab) or a cement-sand mixture. The water level must always be 20 cm above the filling level.

When the water reaches the outlet, its access is blocked and backfilling continues to the level of the top of the tank. Now you should make the thermal insulation of the top, if it is above the freezing level of the soil, connect the shaft to the inlet and fix it (silicone plus self-tapping screws).

Further backfilling is carried out already with soil. The cement-sand mixture will set for three days.


Clay soils are prone to frost heaving. As a result, the «body» of the septic tank can be pushed to the surface. It is more difficult to equip this kind of sewerage on clay soils, but it is possible if:

  • do not neglect the technology (concrete cushion + reliable «anchoring»), so as not to surface
  • deepen the septic tank as little as possible so that conditionally purified water has the opportunity to soak into the soil (in clay, the deeper, the denser the layers)
  • be sure to insulate the part that is above the freezing level of the soil.

There is a suitable option for the purification of a clay septic tank, which is a distribution of drainage pipes with a ventilation device at the end of each. Pipes are laid on a crushed stone pillow, covered with a layer of geotextile.

But once every 5-7 years, such a system requires flushing or replacement.

What else to read on the site:

Thermodynamic heating system

Traditional water heating, in my opinion, has a number of disadvantages associated with the unpredictability of prices (this is the case with gas) and the lack of continuity of the cycle (when they heat with wood or coal). You can, of course, install a boiler with …

Elements of a solar power plant: what and how much you need

Solar energy is perhaps the most effective direction of autonomous energy supply for a private house. The unpredictability of tariffs, the disgusting quality of service provided by Oblenergo to settlements located …

Site drainage, storm drain

Water nourishes all life on Earth. And if the question of how Life originated still causes fiery debate, then the assertion that Water + Sun = the basis of the existence of a biosystem, is accepted unconditionally. However, all is well…

Modern way of life is hard to imagine without a car. And if for a resident of a metropolis a personal vehicle is to some extent an element of luxury (in terms of wasting time in traffic jams), then for a small city …


Добавить комментарий