Maintaining Your Wastewater Treatment System or Septic Tank 

Homeowners should be aware of their responsibilities with regard to the maintenance of septic tanks and other wastewater treatment systems. Septic tanks and other domestic wastewater treatment systems must: 

  • Be registered with 
  • Not pose a risk to human health or the environment; 
  • Not release waste water other than as designed or intended; 
  • Be maintained; 
  • Be emptied periodically; and 
  • Not be open to roof water or surface water. 

These are legal requirements. 

Mechanical plants should be serviced by a professional every 12 months or as per the manufacturer’s instructions. A professional should be engaged for any significant maintenance or if there are significant problems with septic tank systems. 

How often does my septic tank have to be emptied (de-sludged)?  

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

The following table can be used to find out how often you need to empty your septic tank system. This depends on the number of occupants in the home and the tank size. Assume the tank is 2.5m³ if you do not know its size.  

Tank Useable Depth (m)Number of occupants 

Example:  A 3.5m3 tank for a 3-person house needs de-sludging every 4 years. 

Mechanical plants should be emptied as recommended by the manufacturer. 

You must use an authorised waste collector only to empty/desludge your system. You can check online with the National Waste Collection Permit Office.  Farmers can de-sludge their own system only and they must comply with all legal rules or directions. 

For further information or any other queries you may have regarding protecting water quality, please contact the Environment Section of Cavan County Council by phone on 049 437 8486 or by email at