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Holding tanks for holiday rentals and campsites: planning for peak demand

A family home fills its tank at much the same pace every week. A guest house, holiday village or campsite does not: half-empty in May, then a full Midsummer weekend sends cubic metres a day into the tank — often with nobody watching the level. A sewage holding tank (reoveemahuti; in legal texts reovee kogumismahuti) only stores wastewater until a tanker pumps it out (purgimine): no treatment, no outlet. UK readers may know it as a cesspool or cesspit. A holding tank for campsite or holiday-rental use is therefore sized for the busiest days, not the average ones. Below: the peak-load arithmetic, Vesmaco’s larger models, several tanks side by side and alarm relay outputs.

The peak-load calculation: guests × nights

The ministry’s 2015 guide on rural wastewater systems asks planners whether the load is even through the year or seasonal — seasonally used accommodation is its own example. A guest business needs two numbers:

peak daily inflow (L) = guests at full occupancy × litres per guest per night season volume (m³) = guest-nights in the season × litres per guest per night ÷ 1000

The first sizes the tank, the second sets the emptying budget. Both feed the standard method from What size sewage holding tank do you need?:

days between emptyings = usable volume (L) ÷ daily inflow (L) emptyings per season = season days × occupancy share ÷ days between emptyings at full occupancy

Litres per guest. The best input is your own water meter: read it before and after the busiest week and divide by seven. The fallback is the guide’s planning range of 100–150 L of wastewater per resident per day. The guide has no figure for guests; applying the residents’ range to guests in self-contained cabins (own WC, shower, kitchen) is this article’s assumption. For pitches with a shared sanitary block, or day visitors, measure a season or ask a designer. Add whatever else drains to the tank: a sauna house, a hot tub, bed-linen laundry, a café kitchen.

Days to fill at full occupancy, at 100–150 L per guest per night; usable volume = nominal volume for simplicity. The real usable volume is somewhat below the nominal volume because the alarm level leaves a reserve, so check the alarm height on the drawing for your model.

Guests at full occupancy Peak inflow 10 m³ 15 m³ 2 × 15 m³
8 (one large holiday house) 0.8–1.2 m³/day 8.3–12.5 days 12.5–18.8 days 25–37.5 days
20 (for example five cabins) 2–3 m³/day 3.3–5 days 5–7.5 days 10–15 days
40 4–6 m³/day 1.7–2.5 days 2.5–3.8 days 5–7.5 days

Season example (illustrative inputs — use your booking data): 20 beds × 90 nights × 60 % average occupancy = 1080 guest-nights, or 108–162 m³. With a 10 m³ tanker that is about 11–16 loads. Then season cost = loads × your local price per load, or × m³ if the operator charges by volume. A bigger tank does not reduce the volume to be removed; it buys time between visits.

From peak inflow to tank volume: the days you must bridge

volume needed = peak daily inflow × days you must bridge

That is the longest realistic gap between tanker visits in high season. Ask local emptying companies about their lead time in July, whether they work at weekends and over Midsummer (jaanipäev), the tanker’s capacity, and whether they charge per visit or per m³. Twenty guests and four days means 8–12 m³.

The tanker limit. The ministry guide notes that small tankers hold 4–5 m³ and the largest about 10 m³, so a full 15 m³ tank takes two loads. It need not run full: served by a 10 m³ tanker, a 15 m³ tank works as 10 m³ of working volume plus 5 m³ of buffer — for 20 guests, 1.7–2.5 extra days if the tanker is late.

Vesmaco’s larger horizontal fibreglass (GRP) models, values as displayed in the model table:

Model Volume Diameter Length (about) Weight
MK-10 D1400 10 m³ 1400 mm 6.7 m 500 kg
MK-10 D1600 10 m³ 1600 mm 5.3 m 480 kg
MK-12 D1600 12 m³ 1600 mm 6.3 m 560 kg
MK-15 D1600 15 m³ 1600 mm 7.8 m 750 kg
MK-15 D2000 15 m³ 2000 mm 5.2 m 800 kg

A larger diameter gives a shorter tank but a deeper excavation. The listed range ends at 15 m³; for more volume, ask the supplier about your options or plan several tanks (below). Options such as risers, hatches, ventilation and inlet are marked on the order drawing; check the drawing for your model.

Several tanks side by side

When peak inflow × days to bridge exceeds 15 m³, or one long pit does not fit the site, Vesmaco’s installation guide provides for several tanks: at least 50 cm between tanks, anchored to a reinforced-concrete slab or concrete blocks whose weight and dimensions are determined by a certified design or construction organisation.

Footprints follow from the model table. Two MK-15 D2000 tanks: 2.0 + 0.5 + 2.0 = 4.5 m wide, about 5.2 m long; two MK-15 D1600 tanks: 3.7 m × about 7.8 m. Applying the guide’s green-area safety zone (1 m larger than the tank in every direction) around the pair — our reading of the guide — gives 6.5 × 7.2 m and 5.7 × 9.8 m, before excavation working space.

Two layouts to compare with your designer:

  • One group of tanks on a common inlet — a large buffer at a single tanker stand. Ask the supplier how the tanks are connected and whether each needs its own emptying riser, vent and alarm.
  • A tank per building or zone (sanitary block, cabins, main house) — shorter pipe runs, and a fault affects one zone only; but every tank needs its own tanker access and alarm.

An alarm that reaches whoever is on duty

The ministry guide calls a level sensor advisable; where the people filling the tank are not the people responsible for it, it is hard to do without. The wireless Tank-Check RF-431 listed on Vesmaco’s site pairs a transmitter and level sensor in the tank with a mains-powered receiver indoors. Per its manual, the level alarm (buzzer, red lamp, relay 1) activates two minutes after liquid reaches the sensor; a no-connection alarm (relay 2) follows about 30 minutes without updates and also warns of a low transmitter battery.

  • Receiver location. Not in a guest cabin — guests will not act on a buzzer — but at reception or in the owner’s house. Stated range is 100 m; the manual recommends a link test beyond 70 m or where buildings obstruct the signal.
  • Relay outputs. The two potential-free relays (max 24 V, 3 A DC) are meant for external alarm devices — for example a signal lamp at reception or a third-party GSM notifier. Selection and wiring belong to your electrician. Vesmaco’s site also has a sheet for the Vesmaco Cesspool Alarm, built on the same concept; compare the datasheets or ask the supplier which suits your site.
  • One set per tank. Each receiver reacts only to its own transmitter.
  • Alarm level = lead time. The free volume left when the alarm sounds must cover peak daily inflow × tanker response days: for 20 guests and two days, 4–6 m³. The sensor hangs on a 1.5 m cable, so the lowest possible alarm level depends on riser height and tank diameter; check the drawing for your model and ask the supplier what alarm level, and free volume above it, you can achieve.

In peak weeks, book the tanker on a fixed rhythm and keep the alarm as the backup. Alarm types are compared in Sewage holding tank level alarms.

On site: vehicles, covers and paperwork

Vehicles. The ministry guide says the tanker must reach the tank in every season but never drive over it, and that a holding tank must not be installed under a road or parking area. On green areas, Vesmaco’s guide requires that nobody can drive over the tank by accident, with a safety zone 1 m larger than the tank in every direction — on a campsite, a fence or boulders — and it permits trafficked areas only with a reinforced-concrete load-distribution slab (at least 15 cm thick, at least 50 cm above the tank, extending 50 cm beyond it on every side) and a suitable EN 124 hatch. That design belongs to a qualified designer.

Covers and odour. Where guests and children have access, ask the supplier which cover suits the place and whether it can be locked. Near terraces and pitches, consider the vent pipe with a carbon filter offered on the order drawing.

Paperwork. Under the Building Code, installing a holding tank needs a building notice (ehitusteatis, Annex 1), filed through the Building Register (ehitisregister) at least 10 days before work starts, and a use notice (kasutusteatis, Annex 2). For a multi-tank installation at a business, confirm with your municipality which notices it expects. Your municipality’s on-site wastewater rules (reovee kohtkäitluse ja äraveo eeskiri, Water Act § 104(7)) may add setback (kuja), documentation and proof-of-emptying requirements — Saaremaa, for example, requires a receipt from the emptying company each time. Check your own municipality.

When the numbers argue against a holding tank

A holding tank’s running cost is emptying, and at guest-site volumes it dominates. The ministry guide’s planning table considers holding-tank systems for loads of 1–5 and 6–15 residents and rates them as not a sensible solution for 16–50. That describes year-round loads; a 30-bed site open ten weeks is a different case, and the season-volume formula shows where you stand. The guide adds that combined biological treatment systems may suit tourism and accommodation establishments whose load swings 40–50 % over one-to-two-month periods.

Whether an own treatment plant (omapuhasti) is allowed is a legal question first. Water Act § 124 prohibits it in a sewage collection area (reoveekogumisala) of 2000 population equivalents or more; elsewhere, where there is no public sewerage, it may be built — subject to site conditions and the municipality. Otherwise the leak-tight holding tank remains the lawful route. See Holding tank, septic tank or treatment plant.

Frequently asked questions

More cabins are planned in a few years. Should the full volume go in now? The ministry guide advises assessing the load 5–10 years ahead. As Vesmaco’s guide allows several tanks at least 50 cm apart, you can reserve space and a pipe route for a second tank. Adding it later means a second excavation and most likely a new building notice — confirm with your municipality.

Does the rule about holding two weeks’ wastewater apply to a guest house? Only where § 47 of the Public Water Supply and Sewerage Act (ÜVVKS) applies: in a collection area of 2000 p.e. or more, to a person who cannot connect because public sewerage is missing. § 47(2) excludes industrial and manufacturing companies and does not mention accommodation businesses, so ask the water company. Where § 47 applies, the tank must hold at least two weeks’ wastewater (§ 47(7)) — 28–42 m³ at a 20-guest peak, although the Act gives no calculation method — and the water company’s emptying service is available twice per calendar month (§ 47(10)), charged at the same per-m³ rate as for customers connected to public sewerage in that area (§ 48(2)). An English translation of the Act is on Riigi Teataja; only the Estonian text has legal force.

What happens to the tank when we close for the winter? See Sewage holding tanks for summer houses. In short: where groundwater can be high, do not have the tank pumped dry by reflex when you close — groundwater can lift an empty or half-empty tank, which is why anchoring is settled at installation.

Send guest capacity and season length for a proposal. Tell Vesmaco the number of beds or pitches, the maximum number of guests, the season length and busiest weeks, water-meter readings if you have them, inlet depth, groundwater conditions, nearby vehicle traffic and the size of your local tanker. Vesmaco manufactures the tanks, advises on and designs the solution and delivers across Estonia; installation and emptying stay with your installer and your local emptying company. Use the quote form — it has a company field and accepts attachments such as a site plan — or call +372 641 8550.

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