Sewerage for a private house: stacks, outdoor run and connection

Sewerage for a private house: two parts of one system

Sewerage for a private house has an internal part, the soil stacks and branches from fixtures, and an outdoor part that carries wastewater from the house to the city main or a septic tank. Both parts work by gravity, so what matters most is falls and venting. Get the fall wrong and pipes block; forget the venting and the house smells and traps gurgle.

Inside the house: stacks, falls and venting

Pipes from basins and showers are laid to a fall of 2–3 cm per metre, from toilets at least 2 cm. We try to stack bathrooms one above another so that one soil stack is enough. The vent stack is taken above the roof: the drainage breathes through it, and traps are not sucked dry when water is flushed. Where a roof outlet is impossible, we fit air admittance valves. At bends and at the base of stacks we leave access points to clear the pipe without opening the wall.

Stacks in living rooms and next to bedrooms are low-noise or insulated, otherwise the sound of flushing carries through the whole house. Before the boxing is closed, the system is flushed with water and the joints are checked.

Outlet and outdoor run

The outlet from the house passes through the foundation in a sleeve laid before concreting. From there the run goes in a trench on a sand bed, falling towards the main or septic tank. At bends, at changes of diameter and on long sections we install inspection chambers. The depth is chosen so that the pipe will not be crushed by vehicles, and in the mountains below frost depth. Before backfilling we photograph the run and record depths, so it can be found years later without digging.

• outdoor pipe rated for burial, with rigid rings;
• a fall without sags, on a sand bed rather than soil with stones;
• chambers at bends and every 15–20 m of straight run;
• a grease trap on the outlet from the kitchen of a guest house or restaurant.

City mains or a septic tank

In the city a house is connected to the Batumis Tskali main if there is one in the street and wastewater can reach it by gravity. Out of town and on new plots there is often no network, and then we install a septic tank or treatment plant. How to choose between them is discussed in the comparison of a septic tank and mains sewerage.

When the house is below the main

If the plot lies below the road or a basement bathroom is lower than the chamber, wastewater cannot leave by gravity. Then we install a sewage pumping station: a tank with a macerator pump that pushes wastewater through a pressure pipe. The station needs its own power circuit, and for a house with frequent power cuts, backup power or a tank with several hours' reserve.

Rainwater kept separate

We do not let water from the roof and paths into the foul drainage. In a downpour the volumes are so large that pipes and septic tanks overflow, and connecting storm water to the city foul network is not allowed. Rainwater is collected by a separate system into channels, drains or a storm sewer; more on gutters on the gutters page.

How much sewerage for a private house costs

An outdoor PVC sewer of 110–160 mm in a trench with materials costs from 115 ₾ per linear metre. A turnkey drainage point in the house from 210 ₾, an inspection chamber from 750 ₾, a connection to the mains sewer from 4 500 ₾. A sewage pumping station from 5 580 ₾, a turnkey septic tank from 4 140 ₾, site drainage from 87 ₾ per linear metre. The water company's connection fee is not included in our prices. The final cost is set after a site visit and an agreed estimate.