Do-it-yourself monolithic concrete septic tank: schemes and rules for arranging a concrete septic tank

Nikolay Fedorenko
Checked by a specialist: Nikolay Fedorenko
Author: Sonya Lustik
Last update: March 2019

The optimal solution for organizing the treatment of domestic wastewater in private households is a monolithic concrete septic tank. To install it, you can attract a team or do it yourself. This will further reduce the budget, agree? Materials for his device are easy to purchase in hardware stores.

We will tell you in detail how to build a monolithic septic tank. Let's figure out which option of a concrete treatment plant is better to choose for your site. Here you will learn how to care for an autonomous sewer system, what to do with sewage treated in a septic tank.

For independent home masters, we offer step-by-step instruction. A clear perception of information will provide useful schemes, collections of photos and video instructions.

Typical monolithic septic device

Standard concrete septic tanks for cottages and houses have from one to three adjacent chambers. Between them there is a movement of drains through overflow pipes mounted in partitions.

Due to multi-day sedimentation, separation of insoluble sediment from water and the activity of microorganisms, natural wastewater treatment occurs. All septic system chambers are used only for sedimentation.

Do not make the adjacent filter well. Over time, this will lead to deformation of the entire septic tank, so you need to install a filter system separately. It must be selected based on the area and the desired cleaning quality.

It can be a freestanding well, a filtering trench or filter field. The cleaning system can be mounted after the installation of a monolithic septic system, but in this case, trenches will have to be digged manually. Using the equipment will be impossible, the way it can damage pipes and ceilings.

The specifics of a single chamber cleaning station

A septic tank that has one chamber is called a drain pit. Its device does not involve multi-stage cleaning and serves primarily to store sewage and subsequent pumping.

Pumping and transportation of waste is carried out using a special machine. The disadvantage of such a drainage system is its fast filling and costly maintenance.

Scheme of a single chamber septic tank
In a single-chamber septic tank, the settled water flows into the sewer and is further treated in the filtration field or filter well. Solid fractions deposited to the bottom should be pumped out every 4-6 months

The depth on the scheme of this concrete septic tank is 2 m, it is designed to serve two to three people. Due to the lack of cleaning and draining, the tank quickly overflows.

An alternative to a monolithic single chamber septic tank is cesspool of concrete rings, with the features of the construction of which we recommend that you familiarize yourself.

Diagram of a two-chamber version

In this system, water undergoes preliminary sedimentation before discharge or pumping. According to sanitary standards, such water can be discharged into the ground. The advantages of this system are its compactness. With the same volume, two separate tanks made of reinforced concrete rings take up more space than a monolithic concrete structure.

Scheme of a two-chamber septic tank
The diagram shows the proportions of the septic system. The optimal size of the receiving chamber should exceed the volume of the second settling tank in the proportion of 1: 3 (+)

This septic tank has an internal partition made of concrete, which allows water to settle in two stages. In addition, it can be equipped with a sensor that signals an overflow.

The second overflow at the opposite end of the tank is located slightly lower than the first, which eliminates the return of effluents to the receiving compartment and provides spontaneous overflow of the settled liquid into the next chamber.

Scheme of construction of a two-chamber septic tank
A two-chamber drainage pit needs to be pumped out once a year, a single-chamber pit - with a frequency of once every 3-6 months, i.e. 2-3 times more often. Two-chamber will require more construction costs, but in the long run, exceeding the budget will quickly pay off

About how to build a two-chamber septic tank using concrete rings, written here. We recommend that you familiarize yourself with this material.

Necessary tools and materials

For the installation of a concrete septic tank with your own hands, you will need the following materials:

  1. ASG (2.5 t).
  2. Cement (18 bags of 50 kg each).
  3. Liquid bitumen (20 kg).
  4. Iron Corner 40 x 40 (25 m).
  5. A sheet of iron 2 mm thick 1,250 x 2,0 m (1 pc.).
  6. Sheets of plywood 1.5 X 1.5 m (8 sheets).
  7. Flat slate 1500x1000x6 (6 L).
  8. Polyethylene film (two to three cuts with a total area of ​​13 x 9).
  9. Boards 40 x 100 mm.
  10. Plasticizer (depending on type per 5.9 cubic meters of concrete).
  11. Wire rod with a cross section of 0.6 mm (footage depends on the density of the mesh).
  12. Bars 50 x 50 mm.
  13. Bricks (120 pcs.).
  14. Pipes for external sewage (individually, depending on distance).
  15. Pipes for internal sewage (individually, depending on the design).
  16. Branch pipes (individually, depends on a design).
  17. Fittings (according to the number of pipe joints).
  18. Sealant (1 pc.).
  19. Screws (300 pcs.).
  20. Cutting disc for metal (1 pc.).
  21. Grinding nozzle for angle grinder (1 pc.).

To install a concrete septic tank, you will need the following tools and equipment:

All calculations of materials were performed for a monolithic concrete septic tank with dimensions: width -2 m, length - 3 m, depth - 2.30 m.

Monolithic septic system device

The complexity of installation makes many people buy ready-made reinforced concrete structures. Their use allows installation much faster.

It will take a couple of days to organize a septic system of prefabricated elements, and for the installation of a monolithic concrete structure it will take more than a month, including the construction of formwork and a technological break devoted to hardening of concrete stone.

Each stage, from excavation to welding hatches, is carried out in strict sequence. Before you begin to work, you need to stock up on time or agree on assistance with other people on a commercial basis.

Since the pipe leaving the house / bathhouse and entering the septic tank must be laid with normative bias, it is better to prepare a trench for it in advance. This is necessary to accurately determine the height of the pipeline entry into the concrete structure.

Excavation development and preparation

Since the pit will be used as a shape, it is necessary to make its edges as even as possible. Digging should be done without using equipment or using only at the initial stage.

You need to align the edges of the pit manually. Periodically check the flatness of the surface. To do this, use the level. For even corners, periodically you need to measure with a building corner.

Excess soil should be removed or distributed evenly over the site. After completion of excavation, it is necessary to lay a plastic film at the bottom of the pit. It can consist of several cuts.

The film should cover the pit completely. The use of polyethylene performs two tasks. It reduces the consumption of cement mortar, and also serves as additional waterproofing. Joints of plastic sheets do not need to be sealed. The film can be fixed with bricks, so it will not move with strong gusts of wind.

Excavation pit for septic tank
To descend into the pit, you can put together a ladder from improvised materials. With significant recesses on the stairs, soil can be transported in buckets

Construction of formwork for pouring the mixture

The life of the entire structure depends on how the formwork is exposed. Since the volume of liquid will be contained inside the tank, it will exert pressure on the walls of the tanks. Therefore, before exposing the formwork, it is necessary to make reinforcement.

To do this, you can use reinforcement, knitting wire or already finished mesh. Reinforce the walls so that the grid is in the middle of the monolith. Its distance from the outer edges of the pit should be 7 cm.

Pit waterproofing in a pit for a septic tank made of concrete
After the walls, a mesh for the partition is mounted. It must be placed at a distance of 2 meters from the sewer pipe. There should be two compartments. Larger for primary sedimentation, and smaller for secondary

After installing the partition, you can reinforce the floor. The mesh for him should be raised 7 cm from the bottom surface. This is necessary for the greatest bonding effect.

The construction of the formwork is done before the device of the reinforcing frame. To do this, you need to build shields from plywood and bars. It should be two boxes without a bottom. Each is placed in a container.

Their sizes:

  • for the first tank: width and length 1.7 m;
  • for the second tank: width 1.7 m and length 0.085 m;

It is necessary to check that there are no gaps during installation. After organizing the formwork and before concreting, you need to make the installation of overflows. If you do this after concreting, you have to hammer holes. This can lead to structural deformation.

Installation of overflow pipes

For overflows, two straight nozzles are required. The first nozzle is put on sewer pipeleaving home. To do this, cut out a suitable hole in the plywood and bring the end to the receiving tank

The pipe is attached to the pipe with a rubber ring and sealant. The drain hole of the nozzle should face down.

On the partition between two containers, you must insert a pipe 40 cm long.The pipe is fixed in plywood on both sides of the containers. On the ends of the pipe on both sides of the pipe fittings directed downward drain holes.

Preparation and pouring of concrete mortar

Since the layer thickness is small (15 cm), it is necessary to make a strong solution. First you need to take a container for mixing the solution. At its bottom, place cement and ASG, in a ratio of 1: 3.

The amount of water depends on the moisture content of the gravel mixture. The consistency of the solution should be moderately thick. To improve the properties of the solution, you need to use a plasticizer. The amount of its addition depends on the brand of cement.

Cement mortar
For the convenience of pouring cement into narrow gaps between the formwork and the plastic film, you can use a gutter made of metal, a half pipe, or a gutter. This will evenly fill the solution, avoiding the formation of cavities

So you can speed up the filling process. It is better to fill the entire volume in one day. Such monolithic concrete will last longer, since in the cement stone there will be no delamination along the pouring border on different days.

You can start with walls or floors. This is not of particular importance. After the completion of concrete work, you need to wait until the mortar has completely set and solidified. For this, according to construction standards, 28 or several more days.

The curing rate depends on the ambient temperature. When dried, the concrete changes color and becomes lighter. The construction poured into the formwork must be protected from drying out with wet sawdust or polyethylene.

The freezing of cement stone during the hardening period should be completely excluded. At the end of the specified period, you can dismantle the formwork.

Top floor device

Installation of the upper floor begins with the exposure of the frame.

It consists of iron corners, which are installed in the following lock:

  1. Four corners 3 meters long, you need to lay on the walls of the septic tank. One corner from each edge and two close to each other in the middle of the tank.
  2. Several transverse corners are stacked on top, forming a lattice. They need to be stacked taking into account the sizes of future hatches.

The resulting design needs additional fastening. To do this, make holes in the corners and use anchors to attach them to the concrete base. Cross corners need to be attached with bolts or special screws.

After mounting the corners, it is necessary to cut suitable squares from the flat sheet slate. After that, the slate sheets need to be laid on top of the grate. To prevent the flow of the solution, it is worth treating the joints with liquid bitumen.

Next, you need to fence the perimeter of the hatches with boards. Better to make them contiguous. In addition to hatches, put formwork over the entire floor area. After that, you need to insert the ventilation pipe, making a hole in the slate above the second chamber.

Upon completion of the installation of the pipe, it is possible to fill in the overlap area with the solution. After drying and hardening of the solution, formwork must be removed.

Installation of hatches
The empty space for hatches must be covered with bricks, so that they do not rise above the surface. The mortar for bricks must be made without filler, using cement and sand

Since the amount of sand required is small, you can sift the ASG. The proportions of the solution can be done 1: 4. After masonry, it should harden. It takes 2-3 days. After waiting for this period, you can warm and bury the pit. Periodically, you need to compact the soil.

Manhole cover manufacturing

In order to prevent overcooling of the septic system and debris, it is necessary to install hatches. Covers for them can be made of wood and metal. The wooden lid is installed as the inside.

It protects against temperature differences, and a heater is placed on it. For its manufacture, you can use plywood or individual boards, knocked together.The cover does not need to be mounted on awnings, it must be removable.

The outer cover must be made of metal. To do this, you need a building angle (40x40). A rim for the hatch is welded from it, which is attached to the base using anchors.

According to the size of the rim, a cover must be cut from a sheet of metal. Edges need to be processed with a grinding nozzle for angle grinder. Awnings must be attached to the cover. They can be welded or bolted. After that, the cover is attached to the rim in the same way.

Arrangement of the neck of a homemade septic tank
For the necks of a homemade septic tank, you can make two or one common lid from the board. It will have to be changed periodically. The area around is filled with soil, and the lid is closed with water-repellent material

Proper septic system care

During operation, any sewer pipes are periodically coated inside with greasy coating, which reduces their throughput. It must be removed by special means.

They can be chemical or bacterial. Microorganism based products it is preferable, since they do not spoil the pipes and do not lead to the death of microflora inside the septic tank.

In winter, when the temperature drops to -25 degrees Celsius, it is necessary to insulate the holes of the hatches. Otherwise, the processes of organic processing in tanks will slow down, which will lead to a decrease in purification.

How to use treated drains?

The water purified and disinfected in a septic tank can be used to organize the irrigation of plants and trees in a personal plot. It has a small percentage of pollution (10 -15%).

Purified water is quite suitable for domestic use. This will significantly reduce water consumption for the organization of irrigation of the garden or garden in the summer. That means it will save money.

Solar battery
The use of pumping equipment involves power consumption. To provide power, you can use a small solar battery and a battery

For a couple of years of operation, the system will fully pay for itself, since with the help of solar energy converted into electricity, it is possible to reduce the consumption of electricity supplied by centralized networks. Solar battery quite able to meet the needs of the pump.

The pump can pump water from a secondary or tertiary sump, as well as excess sludge from the receiving chamber. Pumped sludge can be used in ripening compost. It is used as a standalone fertilizer or as a mixture with other components.

In the compost pit, you can pour the remains of organic matter. It can be fallen leaves, weeds and manure. After three to four years of decay, an excellent fertilizer is obtained that increases the fertility of the soil in the infield.

Conclusions and useful video on the topic

The first video shows the principle of the construction of a concrete septic tank before pouring with cement mortar:

The second video shows the pouring stage, the dismantling of the formwork and the final form of the septic tank:

This is one of the most budget options. Its manufacture is cheaper than the concrete analogue of the rings, not to mention the prefabricated biological treatment plants. The price gap is more than 50,000 rubles, taking into account installation.

Another design advantage is durability. Concrete does not decompose, but is partially destroyed by moisture. This can be avoided by treating the walls of the tanks with liquid waterproofing materials.

Interesting facts about the construction of a monolithic septic tank made of concrete or a story about how you independently filled, please leave in the block below. Ask questions and share useful information here.

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Visitors Comments
  1. Nikolay Sergeevich

    Well, in general, it is accessible and understandable, it will be especially interesting and useful for beginners. I would like to ask some questions or ask advice:
    1. I made a system with soil post-treatment, that is, clarified and disinfected effluents go into the ground. Or will it be more correct to collect and pump out regularly?
    2. They claim that red brick is more durable in such an aggressive environment. Is it so?
    3. Which sewer pipes are preferable: plastic or cast iron?
    Thanks in advance.

    • Through pipes, I believe that cast iron is the last century and it is not worth using it now. Modern plastic pipes are not inferior in reliability, while it is cheaper and easier to work.

    • Expert
      Nikolay Fedorenko

      Good afternoon, Nikolai Sergeyevich. For your questions:

      1. If water absorption of the soil allows you to use a filter well, of course use. The main thing in this case is the remoteness of the well from the foundation of the house. The distance should be at least 5 meters, and preferably about 8 meters. Highly moist soil in winter is subject to swelling and proximity to the foundation is very dangerous.

      2. Yes, red brick is resistant to aggressive environments.

      3. Plastic is more pragmatic. For many reasons:

      - low weight compared to cast iron. Which facilitates, in addition to delivery and installation;
      - installation is much simpler; sockets allow quick connections. Range of angles for the desired degree;
      - the inner surface is smooth, which reduces the risk of clogging;
      - lack of corrosion in comparison with cast iron. Warranty period for plastic pipes is 50 years.

      When buying, please note that there are sewers for internal wiring, and there are for outdoor installation. They differ in color: the inside is gray, the outside is orange.