Protect the environment and public health by desludging

Protect the environment and public health by desludging

Septic tanks and other domestic wastewater treatment systems need to be emptied periodically to remove sludge.

Published on: 30 Jul 2021

This is a legal and practical requirement. If the sludge builds up too much, it may affect treatment and block the system requiring expensive repair or replacement works. The law requires homeowners to keep a receipt of de-sludging for five years.

To remove the sludge/empty your system you must use an authorised waste collector. You can check online with the National Waste Collection Permit Office at

Farmers can de-sludge their own system only. The following provides some guidance, to homeowners using contractors and to farmers who apply sludge to their own land, on how to manage the sludge from their system properly.

Frequently Asked Questions

Should I mix the contents of my septic tank with my slurry tank?

No, if you mix the contents of a septic tank with agricultural slurry and spread on agricultural land, a larger area will need to be isolated and unused. You would not be able to use it for grazing for six months or for making silage for three weeks

Can I hire a contractor to empty my tank and spread it on my own land?

Yes, you can spread the contents of your own septic tank on you own land if you comply with the guidelines.

Can I lend my slurry tanker to someone to spread the contents of their septic tank?

Yes, you can lend your slurry tanker to someone but only to empty their own tank and spread the contents on their own land.

How much land do I need to spread the contents of a septic tank?

The average septic tank will hold about 4,000 litres (880 gallons).  If you allow an application rate of up to 3,000 gallons per acre, you would need an area of 0.29 (just under a third) acres for one septic tank.

What is the “setback distance” for spreading?

The required distance between a building, road, streams and so on, and the spreading of slurry is called the “setback distance”.  The setback distances, in metres, for different structures is indicated below:

  • Dwelling houses – 100m
  • Public roads – 10m
  • Streams and drains – 10m
  • Lakes and main river channels – 20m
  • Domestic wells – 50m
  • Public water supplies – 50-300m depending on how much water is used.  This is called abstraction.

Dos and Don’ts

Do limit the area - Limit the area where you spread the contents of your septic tank to a small area of the farm that for at least six months is not going to be used:

  • For food production or
  • Silage

The area where you spread sludge should also be fenced off from livestock for at least six months.

Do know your soil - You should know the nutrient management plan and soil analysis of the land on which you are spreading sludge. You should make sure to avoid spreading excessive nutrients.

Do know requirements of the quality assurance schemes - You should know that if you are taking part in a quality assurance scheme, you may be prohibited from spreading any septic tank sludge on your lands. Before applying any septic tank sludge on your land, it is important that you check with companies that you do business with to make sure that this complies with any quality assurance schemes they have.

Do use a permitted contractor - Use a permitted contractor to de-sludge your septic tank or wastewater treatment system and make sure that you have receipts for the work they carry out.  You will need to produce these if your system is inspected 

Don’t spread sludge from other tanks - Do not transport or spread the contents of sludge from other septic tanks onto your land.  Only a permitted contractor is allowed to do so.

Don’t spread near harvesting - Within 10 months before harvesting or during harvesting, do not spread untreated sludge on land where:

  • Fruit is grown (other than fruit trees)
  • Vegetable crops are grown
  • It is intended to cultivate fruit or vegetable crops that are normally on direct contact with the soil and eaten raw.

Don’t spread on crops - Do not use untreated sludge on any crops including

  • Cereals
  • Fodder
  • Sugar beet
  • Fruit trees

You may only apply untreated sludge when you work it into the land during cultivation or inject it into the soil before planting.

Don’t spread during or after rain - Do not spread untreated sludge during or after a period of rain or if rainfall is forecast in the next 48 hours.