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Regular maintenance

Septic tanks

A septic tank must be pumped out (desludged) regularly to remove excess sludge and scum. If the septic tank is not desludged often enough, excessive solids and fats will cause clogging of your disposal system and its early failure. The effluent filter fitted to your septic tank outlet should also be cleaned when your septic tank is desludged.

It should be noted that replacing a failed disposal system can cost over ten times as much as getting a septic tank desludged.

How often a septic tank needs to be desludged depends mainly on the number of people using it and the size of the tank. For households with two to four people, a standard-size septic tank may need to be desludged approximately every three to five years. If your septic tank has an effluent filter on the outlet, then it may need to be desludged less often. However, it is a good idea to have the sludge levels in your septic tank checked approximately every three years to determine when desludging will be necessary. For motels and camping grounds, or for larger communal tanks serving several houses, septic tanks may have to be desludged more often.

A septic tank is desludged by putting a suction hose through the access lid – not down the “mushroom vent” – so keeping the access lid accessible and not covered over is very important. Also, never wash out your tank after it has been desludged, as the bacteria and solids left behind are required to restart biological activity.

If you need advice, contact your local cleaning contractor or your District Council plumbing and drainage inspector.

Aerated Wastewater Treatment Systems (AWTS) and other mechanical treatment systems

All AWTS and other mechanical treatment systems require regular service and maintenance checks by a suitably qualified person to ensure the system continues to work properly. The manufacturer of the system, or their authorised agent, will have a service and maintenance contract that must be entered into when the system is installed. This service and maintenance contract should also cover the disposal system, especially if it is a dripper irrigation line system. A well maintained and operating system will help reduce the build up of slime within the irrigation lines and drippers, thereby reducing the risk of the drippers becoming clogged. There will be an annual fee associated with this maintenance contract.

Sludge will accumulate in the various parts of a system and should be pumped out regularly in accordance with the recommendations of the system’s manufacturer.

Planted disposal areas

If you have an evapo-transpiration seepage system or a planted irrigation line disposal area, then the plants should be well looked after to ensure that they do their job to maximum effect. Maintenance should include replanting and pruning of plants to promote healthy growth.

Distribution box and alternating soakage trenches or beds

Every time you check your septic tank, you should also check your distribution box to make sure all outlet pipes are at the same level and there are no obstructions, such as algal growth. For ease of maintenance, distribution boxes must be accessible and not covered over.

If your disposal soakage trench or bed system has a distribution box that allows you to manually divert effluent from one trench/bed to another, then the trenches in use should be rested at least every three to six months. Alternatively, in some areas – particularly with poor soils – it is recommended that you use all the trenches/beds during the winter months and then rest some trenches/beds during the summer months. Alternating the trenches/beds in use is normally done by adjusting a baffle or valve in the distribution box.

Surface water cut-off drains

If your disposal system is located on a slope, a surface water cut-off drain will usually be installed above the effluent disposal system to prevent stormwater runoff from the slope entering the disposal area. All surface water cut-off drains need to be maintained to make sure they work properly. This may include removing excess grass or plant growth from the drains and making sure there are no other obstructions to prevent the free flow of water.

Prior to winter, it is a good idea to give all surface water cut-off drains a quick visual check and to carry out any required maintenance as soon as possible. If a surface water cut-off drain is not working properly, the excess stormwater entering the disposal area will cause failure of the disposal system and result in effluent flowing down the slope.