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Sewage holding tank connections and ventilation: what needs planning?

A sewage holding tank (reoveemahuti; in legal texts reovee kogumismahuti) stores wastewater until a tanker empties it (purgimine); UK readers may know a sealed tank like this as a cesspool or cesspit. It has no outlet, yet three connections still have to be settled before the pit is backfilled: the inlet from the house, the ventilation, and the service riser with any alarm cable. Most questions concern the holding tank vent pipe: is one needed, where should it stand, and can the building’s own vent stack do the job? This article covers what Vesmaco’s order drawing offers, how to plan the inlet, what municipal rules say about ventilation, and a checklist for the drawing.

What connects to a holding tank

A septic tank (septik) passes settled liquid on to an infiltration field; a holding tank treats nothing and has no outlet pipe. What does connect is listed on Vesmaco’s order drawing, here for the MK-5 D1400 (rev. B, 15.08.2025), where the buyer ticks the options.

Connection Standard Options
Inlet pipe (sisendtoru) PVC, Ø110 or Ø160 (tick one); inlet depth h up to 1500 mm —
Vent connection PVC D110 on top of the tank Vent pipe; vent pipe with anti-odour filter
Service riser (hooldustoru) PVC D200, 500–1000 mm high; plastic cap D400 pipe (500–1000 mm) or D600 shaft (500–1500 mm); EN 124 cover, classes A15–D400
Level alarm — High-level alarm

The Estonian drawing specifies the filter as a carbon filter (söefilter), and Vesmaco’s website calls it odour-neutralising. The base kit listed on the site is the tank, an emptying pipe, a plastic cover and documents.

The inlet: diameter, direction and the joint

Diameter. Tick Ø110 or Ø160 to match the sewer pipe your plumber or designer brings from the building. The drawing shows one inlet, so if a sauna or guest house should drain into the same tank, raise it before ordering: ask the supplier whether a second inlet or another inlet position is possible. Also ask what end the PVC inlet has, so that your installer brings matching fittings.

Direction and depth. On the MK-5 D1400 drawing the inlet enters one end of the tank, 1300 mm above its bottom, while the vent connection and riser sit on top. Turn the inlet end towards the building and keep the riser within reach of the tanker’s hose. The drawing also asks for h, the depth from ground level to the inlet (max. 1500 mm), which follows from the depth of the house pipe and its fall; see How deep should a sewage holding tank be installed? Every model’s drawing is in the model table.

The joint. Vesmaco’s installation guide backfills in compacted 30 cm layers up to inlet level, then connects the pipes, compacting the sand carefully at the connections (steps 6–7). The Ministry of the Environment’s 2015 guide for rural wastewater systems likewise stresses compaction under and around pipe joints. The full sequence is in installation step by step.

Local rules. Municipal rules often cover the pipe too. Saaremaa’s, for example, require the system together with its pipework to be leak-tight and protected from frost (§ 4(1)), and rain and meltwater to be kept out (§ 4(3)). Roof downpipes and land drains do not belong on this pipe; see keeping rainwater out of a holding tank.

Why a closed tank needs ventilation

Every litre that flows in pushes a litre of air out, and stored wastewater gives off foul-smelling gases. Without a vent on the tank, that air can only escape back up the inlet pipe into the building’s drains.

Local requirements are set in each municipality’s rules for on-site wastewater treatment and removal (reovee kohtkäitluse ja äraveo eeskiri), adopted under Water Act (Veeseadus) § 104(7) (official English translation; only the Estonian text has legal force). On ventilation these rules differ. Examples from Riigi Teataja (our summaries; no official English translations of municipal rules exist):

Municipality Provision Ventilation
Saaremaa vald § 4(4) Holding tanks and own treatment plants must be ventilated
Tartu (city) § 4(5) A closed tank and an own treatment plant must be ventilated
Tallinn § 5(1), (8) On-site systems must be ventilated, through the building’s vent pipe or a vent pipe on the system
Kohila vald § 4(6) Required for own treatment plants; holding tanks not mentioned

Check your own municipality’s current rules: whether a holding tank must be ventilated, by which route, and whether a vent-pipe height is set. Where they are silent, the air still needs a route.

Two routes: the building’s vent stack or a vent pipe on the tank

Tallinn’s rules, in the wording in force since 1 July 2026, name both routes and set conditions for each (§ 5(8)):

Through the building’s vent pipe (hoone tuulutustoru) Vent pipe on the tank
How the air leaves Back along the inlet pipe and out above the roof Straight up from the D110 connection
Tallinn’s conditions 0.5 m above the roof surface; at least 1.0 m from a chimney, 8.0 m from a ventilation air intake and 1.0 m from a ventilation exhaust; at least 5.0 m horizontally from a higher window At least 0.7 m above ground; insects must not be able to get in
Material UV-resistant or UV-protected UV-resistant or UV-protected
On the order drawing Ask what happens to the D110 connection Tick “vent pipe” or “vent pipe with filter”

Through the house, the air has to be able to travel all the way from the tank to an open stack above the roof. Ask your plumber or designer to confirm this for your drainage layout, for example that nothing between tank and stack blocks air flow, before you decide against a vent pipe on the tank. In an existing house, have the stack checked first.

A vent pipe on the tank does not depend on the house. Stand it away from terraces, play areas and windows, and outside the tanker’s route: the ministry guide says the emptying truck must not drive over the tank. The filter option suits a pipe that has to stand close to people.

Before ordering, ask the supplier which route they recommend for your site and, if you vent through the house, what happens to the D110 connection on the tank. For the optional vent pipe, compare its height above ground, UV resistance and insect protection with your municipality’s conditions, and ask about the filter type, replacement filters and how often the filter should be changed.

If a finished system smells, causes and remedies are in Sewage holding tank smells.

Alarm cable, service riser and the order drawing

Alarm cable. For an overfill sensor, step 8 of Vesmaco’s installation guide lays a cable protection pipe (kaablikaitsetoru) to the tank and drills a cable entry in the riser wall: easy while the trench is open, hard later. The wireless Smartel Tank-Check RF-431 offered on Vesmaco’s site needs no cable to the house; its guide hangs the sensor inside the tank, fixes the transmitter as high as possible and not under a metal cover, and puts the receiver in the building. Tallinn requires a level sensor with an alarm on holding tanks (§ 5(12)); the ministry guide calls a level sensor advisable. For help choosing one, see holding tank level alarms. If you choose the wireless alarm, ask the supplier whether a conduit is still worth laying and how the cable entry in the riser wall should be sealed.

Service riser. The tanker’s hose goes in through the riser: PVC D200, 500–1000 mm high, as standard, or a D400 pipe (500–1000 mm) or D600 shaft (500–1500 mm). Tallinn requires a service opening at least 200 mm in diameter with a hatch, reaching at least 100 mm above ground on a green area (§ 5(4)–(5)). Riser height follows the inlet depth.

Checklist (row numbers as on the MK-5 D1400 drawing):

  1. Row 2: inlet Ø110 or Ø160, and h in millimetres.
  2. Layout: which tank end faces the house; any second building draining to it.
  3. Rows 3–4: riser size and height; plastic cap, or an EN 124 hatch and its class.
  4. Rows 5–7: venting route; vent pipe plain or with filter, and where it will stand.
  5. Row 8: alarm or not; wireless, or a conduit to the building.

Frequently asked questions

Does a holding tank need a vent pipe? It needs ventilation, but not necessarily a pipe on the tank. Saaremaa and Tartu require holding tanks to be ventilated; Tallinn accepts either the building’s vent pipe or a pipe on the tank. Check your own municipality’s rules.

How high should the vent pipe be? It depends on where you live. Tallinn requires a vent pipe on the tank to reach at least 0.7 m above ground and keep insects out; other municipalities may set a different figure or none, so ask yours.

Is the carbon filter necessary? None of the municipal rules opened for this article requires one. Consider it when the vent pipe has to stand near a terrace, path or window, and ask about replacement filters before ordering.

Select your connection options on the drawing. Download the order drawing for your model from the model table, tick the inlet diameter, riser, cover, vent pipe and alarm, and note the inlet depth h. Then send your choices through the quote form or call +372 641 8550; the site says replies usually come within 2–3 days. Vesmaco manufactures the tank and advises on these options at the design stage; the pipework to the house and the installation are for your plumber and installer.

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