How often to pump a septic tank, holding tank and BIO plant

The short answer: the minimum under the rules

National regulations do not set a specific frequency. They require the contents of septic tanks and holding tanks to be handed over regularly to a pumping contractor, taking into account water consumption, the tank's volume and the minimum set by the municipality. Here's how Riga and the two largest neighbouring municipalities do it:

In Jūrmala and in the Ādaži, Olaine, Salaspils and Ropaži municipalities, the minimum for a septic tank is also once a year. In Ādaži Municipality, at least 70% of the septic tank's working volume must be removed each time. More details for each location are on the pages about Riga and the Riga region.

Septic tank: how to tell it's time to pump

A septic tank lets wastewater settle: heavy particles sink to the bottom, fats and light matter float to the top, and the relatively clear water flows on to the infiltration system. The sediment layer grows every day. If it isn't removed, the sediment starts leaving with the water and clogs the drain field (infiltration field), and that costs far more than pumping.

Signs that the septic tank needs pumping before the next scheduled time:

• drains in the house have become slower, or the toilet “gurgles” when you flush;
• there is a smell around the lid or above the drain field;
• the water level in the tank is above the outlet pipe;
• the ground above the drain field is constantly wet.

In a house lived in all year round with a small septic tank, the municipal minimum may turn out to be too little. If your septic tank fills up fast or smells, look for the cause on the pages septic tank fills up fast and septic tank smells.

Holding tank pumping frequency: the calculation

A holding tank has no outlet: everything you use in the house stays in it. That's why municipalities calculate the frequency with a simple formula: the annual volume of wastewater divided by the tank's volume. If there is a water meter, its readings are used; if not, the assumed consumption per declared resident is used.

Example: 3 residents declared at the house, no meter, an 8 m³ holding tank, no deduction for garden watering.

That is the minimum under the rules. The real frequency depends on how much water you actually use. The easiest way to find out is to compare your meter readings with the tank's volume: if you use 9 m³ a month and the tank holds 8 m³, it will need emptying about once a month. Read more about this work on the page holding tank pumping.

BIO plant maintenance frequency and sludge removal

For a biological treatment plant, national regulations require technical maintenance once a year unless the documentation of the manufacturer, the builder or a suitable company says otherwise; the maintenance is carried out by a company that specialises in such work. Municipalities set the frequency of surplus sludge removal according to the manufacturer's instructions. Examples from manufacturers' documents:

• AUGUST AT: the sludge concentration is measured every 6 months; surplus sludge is removed if there is more than 600 ml per 1 l of water.
• PURA: surplus sludge is removed at least every six months, preferably every two months; servicing at least 2 times a year.
• AQUABLOC: the heavy sludge layer is removed at least once every 2 years; the manufacturer recommends once a year.

A comparison by manufacturer is on the page BIO plant comparison, and for the work itself, read BIO plant maintenance.

What to do with pumping documents

After every pumping, get a document stating the address, the volume collected, the date and the pumping contractor's details, and keep it for at least two years. In Riga, this information is needed for the annual declaration due by 1 May; elsewhere, the municipality may ask for it during an inspection. More: contract with a pumping contractor and pumping certificate.

How much septic tank pumping costs

The price depends on the volume to be pumped, the distance from Riga, the length of hose needed to reach the lid and how thick the sediment is. If the septic tank is pumped on time, the job is quicker and simpler. See all prices on the prices page.