Environmental guidance for your business in Northern Ireland & Scotland

Maintaining your septic tank

Maintaining your septic tank

To keep your tank working effectively you should carry out regular maintenance. You should look out for the signs that problems might be developing by regularly checking:

  • Do sinks or toilets in your house drain slowly or back up? The most likely cause of this is a tank that needs emptying, or desludged. Have the sludge removed regularly to prevent problems. This problem could also be caused by blocked pipes. If your tank does not need desludging but the problem continues you should contact a specialist or plumber who can clear the pipes without using chemicals.
  • Is there a detectable odour where the soakaway is located, with damp ground visible and a flush of green grass? – this could be a problem with the soakaway being clogged, discharging to an area where the water table is too high or the soil has poor natural drainage. A specialist will identify the problem and could provide a solution.
  • Is the discharge from the tank clear and odourless? – if it is dark, contains solids and has an odour then something is preventing the septic tanks from working. This could be a build-up of sludge, blocked pipes, or harmful chemicals have been added to the tank which have killed the bacteria. Have it checked by a specialist.
  • If your tank never needs to be desludged then there is a chance that it is leaking, or you have a burst pipe. You should have this investigated by a specialist or plumber as you could be causing water pollution, or even a health hazard.
  • If there is no outflow from the tank then the drains to your tank could be blocked, or there could be a leak from the tank. Again you must have this investigated to find the cause.
  • Is there a noticeable fungal growth, or an odour coming from a nearby stream or watercourse? This indicates that untreated sewage is finding its way to the water. This could be the result of a damaged or leaking tank or pipes, which are releasing raw sewage. Contact a plumber or drainage specialist to fix the problem.



Over time the solids that settle out build up, effectively reducing the volume of the tank and making it less efficient. You must have your tank regularly desludged.

Check the outflow from the tank, if it is clear and odourless then your tank is working well. If it has an unpleasant odour, is discoloured or has any solids in it then it is likely that your tank needs to be have the sludge removed.

Usually a tank should be desludged once a year and you can arrange a regular service from contractors. If you set up regular visits from a business that carries out desludging, it will help prevent problems, and will usually cost significantly less than an unscheduled visit.

Then frequency of desludging will depend on the size of the tank, the number of people using it, and how well you look after it.


Keep access to your tank clear

Locate the access lid for your tank and make sure it is clear of vegetation and soil. Don’t operate heavy machinery or drive vehicles over the ground where the pipes have been laid. This includes the area of ground used for the soakaway.

Don’t allow trees or deep rooted shrubs to become established close to your tank or the soakaway, the roots can damage the pipework resulting in blockages or leaks. In either case the repairs could be costly.

If you suspect that there is a problem, get a plumber or drainage specialist to check out the tank as soon as possible.


Regular checks

It is important that you regularly check the operation of the system.

  • Carry out a fortnightly or monthly visual check on the discharge from system to the drainage field. Your septic tank should have an inspection chamber fitted between the tank and the soakaway. The discharge should be clear and shouldn’t contain any solids.
  • At the same time check the level of the liquid in the tank. If it is very low then your tank could have a leak. If it is very high then you may have a blocked outlet pipe.
  • Check the area of ground where the soakaway is located. Make sure the ground is not saturated, and that there is no odour. Check nearby watercourses, such as ditches and streams to make sure that there is no fungus or odour associated with the tank.

Figure 2: Sewage fungus in a stream


If you find any problems, have a professional look at the tank and the drainage. Problems that are not fixed can lead to pollution and could cause a nuisance to neighbours.

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