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Sewage holding tank installation step by step: from site preparation to commissioning

The excavator is booked, but what exactly happens in the pit, and which parts fall to you, the installer or the supplier? A sewage holding tank (Estonian: reoveemahuti, in legal texts kogumismahuti; UK readers may know a sealed tank as a cesspool or cesspit) only stores wastewater until a tanker pumps it out (purgimine). It treats nothing and has no outlet, so it must stay leak-tight and in place, whether full or empty. This holding tank installation guide follows the nine steps of Vesmaco’s instructions for fibreglass (GRP) tanks, with why each step matters and who usually does it, and ends with commissioning.

Before digging: notice, drawing and materials

The building notice. Under the Building Code (Ehitusseadustik, Annex 1), installing a holding tank needs a building notice (ehitusteatis), not a building permit. It is filed through the Building Register (ehitisregister, ehr.ee) at least 10 days before work starts, and the municipality may add requirements. Any minimum distance (kuja) and other location requirements come from your own municipality’s rules for on-site wastewater (Water Act § 104(7)), so check them first. Details: holding tank rules in Estonia.

The drawing. Each model in the model table has a drawing (PDF and DWG) that doubles as the order form: inlet PVC Ø110 or Ø160, its depth h (maximum 1500 mm; “installation height” on the English drawing), riser, cover, vent, alarm and straps. The depth follows your house’s sewer pipe; see how deep to install a holding tank; inlet and vent choices are in connections and ventilation.

The guide. Vesmaco’s installation guide (paigaldusjuhend; PDF in Estonian, 26.01.2016, written “according to EN 976-2”) has nine steps and four special cases; ask the supplier whether it is still the current revision. Its preamble, in our translation: anyone without experience of installing tanks should ask the supplier or manufacturer for a list of licensed installers; Vesmaco is not liable for damage in transport or installation; and “if the installation instructions are violated or ignored, the product warranty does not apply.” Give the guide and drawing to every installer who prices the job, and compare offers with what an installation quote should include.

Materials, delivery and season. Vesmaco’s base kit is the tank, an emptying pipe, a plastic cover and documents; the other materials appear step by step below. The Ministry of the Environment’s 2015 guide to rural wastewater systems (official, though dated) says to check the tank for transport damage and follow the manufacturer’s lifting advice. The installation guide does not cover lifting, so ask the supplier how the tank should be lifted before it arrives. Access and unloading: delivery and unloading. Working in frost? Read installing a holding tank in winter first.

Stage Usually done by
Building notice; checking municipal rules You (the owner)
Model, options and inlet depth on the drawing You, with Vesmaco’s consultation
Delivering the tank Vesmaco (delivery across Estonia)
Sizing an anchoring slab or blocks; design for traffic loads A certified design or construction organisation
Steps 1–9 in the pit Your installer
Photos of each stage before it is covered Your installer or you: agree who
Use notice You, or someone acting for you

Excavation and sand bed

Vesmaco’s guide says what to do, not why: the “why it matters” notes are our explanation, using the ministry guide where it gives a reason. Neither guide gives pit dimensions, but the ministry guide asks for room to backfill and compact properly under and beside the tank.

Step 1: a compacted sand bed at least 20 cm thick

The guide: at least 20 cm of stone-free sand, fraction 0–3 mm, levelled and compacted to 95 % of natural density (not less than 1500 kg/m³).

Why it matters: the bed carries the tank for as long as it is in the ground. A stone or a loose patch leaves the shell resting on a few points, and a bed that settles later can tilt the tank and strain the pipe joint.

Who: your installer.

Placing the tank, anchoring and water ballast

Step 2: a slab or blocks for anchoring

The guide: a 20 cm reinforced-concrete slab of frost-resistant concrete, topped with 20 cm of compacted stone-free sand; in stable soil, reinforced-concrete blocks at least 20 cm thick. A certified design or construction organisation sets their weight and size. The guide numbers the slab as step 2 without saying when it can be left out, so ask the supplier whether your site needs it.

Why it matters: an empty tank weighs only 150–800 kg, and in wet ground the water it displaces pushes it upwards. The ministry guide calls a slab and anchoring essential where groundwater is high, so that an empty or half-empty tank cannot rise and be damaged, and warns never to set a tank directly on a hard base: hence the sand on top.

Who: a designer sizes the slab or blocks; your installer builds it. When anchoring is needed: holding tank anchoring.

Step 3: set the tank on the bed and level it

The guide: place the tank on the compacted sand and level it.

Why it matters: a level tank bears evenly on its bed and puts the inlet at the planned height. It is also the last chance to inspect the whole shell before sand covers it.

Who: your installer, with lifting equipment.

Step 4: a quarter full of water, then the straps

The guide: fill a quarter of the tank with water, then fit and tension the straps. Use textile straps only; ask the seller about type and quantity. The MK-5 D1400 drawing offers four polyester straps with tensioners; the manufacturer specifies the number per model, so check the drawing for yours.

Why it matters: water is the weight you can add on site. The guide does not say whether “a quarter” is measured by volume or by height, so check with the supplier. Read as a quarter of the volume, water at step 4 (m³) = nominal volume × 0.25, so 1.25 m³ for a 5 m³ tank and 2.5 m³ for 10 m³. In an MK-5 D1400 that is about 1250 kg of water (1 m³ ≈ 1000 kg) on top of the tank’s own 290 kg, holding it down while the straps are tensioned and the pit is still open to rain or groundwater.

Who: your installer. Agree beforehand who supplies the water.

Layered backfill and pipe connections

Step 5: the first 30 cm layer, under the tank

The guide: with the first 30 cm of backfill sand, carefully compact under the tank and between its support legs.

Why it matters: the space under the curve of the tank is the easiest to leave hollow and cannot be reached once the next layer is on. The ministry guide also stresses compaction at the tank’s sides, ends and pipe connections.

Who: your installer.

Step 6: 30 cm layers up to the inlet, adding water

The guide: backfill in compacted 30 cm layers of stone-free sand up to the inlet pipe, adding water to the tank at the same time.

Why it matters: a 30 cm layer can be compacted through its full depth; a metre of sand tipped in at once cannot. Rising water inside adds weight and balances the sand pressing on the shell from outside. Typical errors are collected in bedding and backfill mistakes.

Who: your installer.

Step 7: connect the pipes

The guide: connect the pipes and compact the sand carefully at the joints.

Why it matters: the Water Act (Veeseadus, § 124(2)) requires a leak-tight (lekkekindel) holding tank, and the inlet joint is part of that seal. A joint on sand that settles later can move out of line and leak.

Who: your installer.

Alarm conduit, riser and hatch

Step 8: a conduit for an overfill sensor

The guide: for an overfill sensor, lay a cable conduit to the tank, drill a cable entry in the riser wall and install the sensor according to its own instructions.

Why it matters: the ministry guide advises a level sensor, and a holding tank must never overflow. A conduit is easy to lay in an open trench, so choose the alarm now. The wireless alarms documented on Vesmaco’s site (Smartel Tank-Check RF-431, Vesmaco Cesspool Alarm) need no cable to the house: a transmitter in the tank signals a receiver indoors.

Who: your installer lays the conduit; agree who fits and tests the sensor.

Step 9: final layers, riser and cover

The guide: backfill in compacted 30 cm layers up to ground level.

Why it matters: sand compacted to the top leaves no soft spot above the tank. The riser (PVC D200, h 500–1000 mm, as standard) must reach the finished ground level, and the cover (plastic, or an EN 124 hatch from class A15 to D400) must suit whatever crosses it. With less than about 1.3 m of cover over the tank or pipe, the ministry guide advises insulation.

Who: your installer. Riser height and cover type are your choices on the drawing.

Commissioning: use notice and records

After the work, a use notice (kasutusteatis, Building Code Annex 2) is filed through the Building Register at least 10 days before the tank is put to use. It names the person who built the tank.

Your municipality may ask for more. Saaremaa, for example, asks for an act of covered works (kaetud tööde akt) with photos, certificates or declarations of conformity for the tank, and its location; undocumented work needs an inspection by a competent specialist, including a leak-tightness test. Requirements differ by municipality, so check your own. Ask the supplier which conformity documents come with the tank, since many municipalities ask for them at commissioning. The ministry guide recommends keeping records anyway: they may be needed when the system is rebuilt or the property is sold.

Before first use, check that the level alarm reports normal operation (a green OK light on the Tank-Check RF-431 receiver) and that the emptying truck can reach the tank in every season. From here on, emptying by tanker is the tank’s running cost.

Special cases: traffic areas, deep installation, several tanks

Green area. The guide’s basic case: no vehicle may drive over the tank by accident, so the safety zone is 1 m larger than the tank in every direction. The ministry guide adds that the emptying truck must not drive over it either; large stones can serve as barriers.

Traffic or parking area. The two guides differ. Vesmaco’s allows it with a reinforced-concrete slab at least 15 cm thick, at least 50 cm above the tank and 50 cm wider on every side, and a hatch class suited to the traffic; if a floating hatch frame is used, it must not rest on the riser. The ministry guide says a holding tank must not go under a road or parking area. A qualified designer should decide: see can a holding tank go under a driveway?

Deeper than 1.5 m. Vesmaco’s guide requires the same slab: at least 15 cm thick, 50 cm above the tank, 50 cm wider on every side. The guide does not say what the 1.5 m is measured to, and the drawing allows an inlet depth of up to 1500 mm, so ask the supplier or your designer whether the slab applies to your planned depth. How the depth is worked out: how deep to install a holding tank.

Several tanks. Keep at least 50 cm between tanks; the guide shows them anchored on a reinforced-concrete slab or on blocks.

Frequently asked questions

Can I install a holding tank myself? Vesmaco’s guide sends anyone without tank-installation experience to ask for a list of licensed installers, and the warranty depends on following its instructions. The ministry’s 2015 guide advises doing it yourself only if you know the rules and can avoid mistakes, since a wrongly installed system can endanger groundwater and drinking water; otherwise, hire a construction company. If you plan to install the tank yourself, ask the supplier for the warranty terms in writing first, including what is covered, the conditions and which records of the work you should keep.

Why is the tank filled with water during backfilling? An empty tank weighs only 150–800 kg, and wet ground can lift it. A quarter-fill (about 1250 kg of water in a 5 m³ tank) holds it on its bed while the straps are tensioned; water added with each sand layer keeps the load inside growing with the load outside.

Which sand should be used for bedding and backfill? Stone-free sand, fraction 0–3 mm, compacted to 95 % of natural density, according to Vesmaco’s guide: at least 20 cm under the tank, then 30 cm layers up to ground level. The guide does not provide for backfilling with excavated soil. The ministry’s 2015 guide, written for tanks in general, also mentions gravel or crushed stone for the bed and sand or gravel for backfill; for a Vesmaco tank, follow Vesmaco’s specification, since the warranty depends on it.

Get the guide and drawing with your quote. When you ask Vesmaco for a price, ask for your model’s drawing and the installation guide too, and give both to your installer before the work is priced. Send the volume, your inlet depth and what you know about groundwater and traffic through the quote form, or call +372 641 8550.

Sources

The English translations on Riigi Teataja are for information only; only the Estonian text of an act has legal force.

Last checked: 17 September 2026.