Septic Tanks and Off-Mains Drainage
Properties not connected to a public sewer treat wastewater on site, usually with a septic tank, a package treatment plant or a cesspool. Each works differently and carries different obligations.
The three types
A septic tank separates solids and allows liquid to discharge to a drainage field, where the ground provides further treatment. It requires suitable ground conditions.
A package treatment plant aerates the effluent and produces a cleaner discharge, which can in some circumstances go to a watercourse. It uses electricity and needs servicing.
A cesspool is a sealed holding tank with no treatment and no discharge. It requires frequent emptying and is expensive to run, generally used only where nothing else is possible.
Regulatory change
Rules on discharges have tightened in several jurisdictions. Discharges from septic tanks directly to watercourses have been restricted or prohibited, requiring either replacement with a treatment plant or connection to a drainage field.
Obligations frequently trigger on sale of the property, which is why this surfaces during conveyancing and delays transactions.
Establish which regime applies locally and whether your system complies. The rules are specific and enforcement has increased.
Maintenance
Septic tanks need emptying periodically — commonly annually, depending on tank size and occupancy — by a licensed waste carrier who provides a receipt. Keep those receipts, since they evidence compliance.
Treatment plants need scheduled servicing, typically annually, plus emptying. The aeration components fail if neglected, and the discharge quality deteriorates without any obvious sign until it is inspected.
Drainage fields have a finite life and eventually clog. Signs include waterlogging above the field, slow drainage indoors, and odour.
What damages these systems
The bacteria doing the work are sensitive. Bleach and disinfectants in quantity, antibacterial cleaners and paint or solvents all reduce their effectiveness.
Wet wipes, sanitary products and cooking fats block systems reliably. Nothing other than waste and paper should enter the system.
Water softener discharge and excessive surface water entering the foul system both overload it.
Buying a property with one
Commission a specific drainage survey rather than relying on a general building survey.
Establish the type of system, its age, the maintenance history, where the drainage field is, and whether any discharge consent exists.
Establish the exact boundary position of the tank and field, since these are sometimes on neighbouring land with rights that need documenting.
Replacement of a non-compliant system is a substantial cost, and discovering the need after purchase rather than before is entirely avoidable with a survey.
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