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2–3 m³ sewage holding tanks: when is a small tank enough?

A small sewage holding tank (reoveemahuti; UK readers may know a sealed tank as a cesspool or cesspit) is tempting: a shorter pit, a lighter tank. But a holding tank treats nothing and has no outlet. Every litre that goes in has to be pumped out and taken away by tanker (purgimine), so volume decides how often you pay for a visit. The short answer: 2–3 m³ suits low-flow, occasional use, and seldom even two people living in the house all year. Below: the two smallest Vesmaco models, the fill-time arithmetic, and where a small tank works or falls short.

The two smallest models in the range

Model Volume Diameter Length Weight
MK-2 D1100 2 000 L 1100 mm about 2400 mm 150 kg
MK-3 D1100 3 000 L 1100 mm about 3500 mm 200 kg

Figures as shown in the model table on reoveemahutid.ee; lengths are approximate, so check the drawing for your model when the pit size matters.

Both are horizontal reinforced-fibreglass (GRP) cylinders in the D1100 family — the narrowest diameter, so the shallowest excavation in the range. The base kit matches the larger models: tank, emptying pipe, plastic cover, documents. Options (inlet, riser, hatch class, ventilation, alarm, anchoring straps) are marked on the order drawing — check the drawing for your model; reading it is covered in holding tank dimensions and drawings.

How fast 2–3 m³ fills for two people

days between emptyings = usable volume (L) ÷ (persons × litres per person per day)

Assumptions: the best input is your own water-meter data (monthly m³ ÷ days). Without it, use the planning range of the Estonian ministry guide (2015), 100–150 L of wastewater per resident per day: 200–300 L a day for two. Usable volume is taken as nominal volume for simplicity. In practice it is somewhat below the nominal volume because the alarm level leaves a reserve, so real intervals are shorter — check the drawing and the alarm height for your model.

Tank Days to fill at 200 L/day Days to fill at 300 L/day Visits per year, two permanent residents
2 m³ 10 about 6.7 about 37–55
3 m³ 15 10 about 24–37
4 m³ 20 about 13 about 18–27
5 m³ 25 about 17 about 15–22

Visits per year = 365 × occupancy share ÷ days. A cabin used by two people two days a week for 26 weeks (52 days, occupancy share about 0.14) needs about 5–8 visits a year with 2 m³ and about 3.5–5 with 3 m³.

Yearly cost = emptyings per year × your local price per visit. Ask local emptying companies how they charge: if it is per visit rather than per cubic metre, emptying 2 m³ may cost as much as emptying a larger tank. The full method is in what size sewage holding tank do you need.

A small tank also leaves little warning. The ministry guide advises ordering the tanker when the level passes about half the diameter — in a horizontal cylinder, half the volume. Two people then have 1 m³ left in a 2 m³ tank (about 3.3–5 days) or 1.5 m³ in a 3 m³ tank (5–7.5 days). If the tanker cannot come within that window, the tank is too small. The guide calls a level sensor advisable; Vesmaco offers an alarm as an option.

Where a small tank is enough

The ministry guide names small or periodic water use as a case for a holding tank. At 2–3 m³ that means:

  • Sauna greywater only — washing water, no toilet. See collecting sauna wastewater.
  • A weekend cabin for two — 3 m³ lasts 10–15 days of use, about five to seven weekends.
  • A dry toilet plus greywater — only washing and kitchen water reaches the tank.

For greywater-only uses, do not borrow the 100–150 L figure: it is a whole-household planning value. Meter your own use and apply days of use = volume ÷ metered litres per day of use.

When 2–3 m³ is too small

  • Permanent living. The ministry guide’s benchmark is a four-person family living permanently: at least 5 m³, emptied about once a week. Four people fill 3 m³ in 5–7.5 days and 2 m³ in about 3.3–5 days. Regular guests shorten the interval in the same way.
  • The two-week rule. If the property is in a sewage collection area (reoveekogumisala) of 2000 p.e. (population equivalents) or more and cannot connect because public sewerage is missing, the Public Water Supply and Sewerage Act (ÜVVKS) § 47(7) requires a leak-tight tank that holds at least two weeks’ wastewater. By the planning range two people produce 2.8–4.2 m³ in 14 days: 2 m³ falls short and 3 m³ fits only at the low end. The rule covers that situation only; ask your municipality or water company how they assess the two-week volume.

One size up from 3 m³ means about a metre more length (MK-4 D1100, about 4.55 m) or a shorter, wider and deeper pit (MK-4 D1400, about 2.9 m). Going from 2 to 4 m³ halves the tanker visits. Ask for quotes on both sizes and weigh the price difference against the tanker visits saved each year. If your numbers point past 5 m³, see 5 m³ or 10 m³.

What does not shrink with the tank

Rules. Annex 1 of the Building Code has one row for holding tanks (reovee kogumismahuti), with no volume threshold: installing one needs a building notice (ehitusteatis) filed through the Building Register at least 10 days before work starts, and Annex 2 adds a use notice (kasutusteatis). Your municipality’s own wastewater rules (Water Act § 104(7)) may add requirements, including a setback (kuja) — check them for your address.

Installation. Vesmaco’s installation guide applies whatever the size: at least 20 cm of compacted stone-free sand under the tank, sand backfill compacted in 30 cm layers while water is added to the tank, and textile straps only for anchoring. It states that the warranty does not apply if the instructions are ignored. With high groundwater the ministry guide calls a concrete slab and anchoring essential — a 150–200 kg tank is no exception. Slab design is a qualified designer’s job; the work is your installer’s.

Frequently asked questions

Is 2 m³ enough for a summer house with a flush toilet? For two people it holds about 6.7–10 days of use: fine for weekends, but on a four-week holiday expect the tanker every week to ten days.

Can any tanker empty such a small tank? By volume, yes: by the ministry guide even small tankers carry 4–5 m³. The truck still needs access in every season.

Can I add a second tank later? Vesmaco’s installation guide allows several tanks at least 50 cm apart, but it means a second excavation, new pipework and a new building notice. Planning the right volume from the start is usually simpler — see what size sewage holding tank do you need.

Check your numbers with us before choosing the smallest model. Send us the number of people, days of use per year, a water-meter reading if you have one and the inlet depth; we will check the arithmetic and suggest matching models. Use the enquiry form or call +372 641 8550 — the site says replies usually come within 2–3 days.

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