Holding tanks

Holding tanks: when they make sense

A holding tank is the simplest type of off-grid sewage system. It treats nothing: wastewater collects in a sealed tank and is removed from time to time by a vacuum truck. Below: when this solution is sensible, what price you pay for it and what needs thinking through in advance.

A holding tank is often called a fit-and-forget solution, but forgetting about it is exactly what you cannot do. Its simplicity rests on one condition: the truck must arrive on time and be able to reach the hatch, in any weather and in any season.

— Editor's note

History of this address

Archived address · now a reference page

This address used to hold a page from a seller of treatment plants describing holding tanks. That site no longer exists, and our guide has no connection with it.

Now it holds an explanation of how such tanks are built and when they make sense. We sell nothing, name no models and publish no prices.

How a holding tank works

Wastewater from the house flows through pipes into a closed tank and stays there. No treatment takes place inside, so the key requirement for the tank is that it is watertight: the contents must not leak into the ground, and groundwater must not get in.

When the tank fills up, a vacuum truck is called to pump it out and take the wastewater away. How often that will be needed depends on the number of occupants, their habits and the capacity set in the design.

Pros and limitations

The design is simple: no compressors or complex electronics that need constant servicing.
It can be a solution where soil or groundwater conditions make treatment in the ground difficult; this is determined by the design.
A holding tank copes with long breaks in occupancy more easily than systems that rely on living bacteria.
On the other hand, pump-outs are needed regularly, and with year-round occupancy the truck visits become frequent.
The owner depends entirely on how available a pump-out service is in the area.

What to consider when siting it

Access for a vacuum truck at any time of year; without it the option loses its point.
Distances to wells, water intakes and buildings are set by sanitary rules and the design, not by advice from forums. Outside Russia, check local regulations and permits.
How the tank is anchored in the ground is chosen based on survey data, especially where groundwater is high.
The hatch must stay accessible, and the area above the tank should not be used for parking or storing heavy items.

Maintenance

Keep records of pump-outs; this makes the next one easier to plan.
Book pump-outs in advance, especially before winter and holidays.
Do not put building waste, wipes or cat litter down the drain.
Report signs of overfilling and smells to the service rather than checking yourself.

What this text is based on

SP 32.13330 "Sewerage. External networks and facilities" (Russian code of practice)
Russian sanitary rules and standards (general provisions)
Equipment manufacturers' instructions (general provisions)

Rules, requirements for treatment facilities and equipment manuals are updated from time to time, so the final word belongs to the design, the regulations in force and the documentation of your particular system. The texts here cite Russian standards; other countries have their own building and sanitary rules, so check local regulations and permits. This guide explains how systems work and why decisions are made, but it does not replace a designer, an installer or a service company.