How a septic tank works
In a septic tank, solids settle at the bottom and fats float to the surface. Bacteria slowly break them down without air. The pre-treated water flows into a soakaway or the next treatment stage.
Why it starts to smell
Bleach, disinfectants, caustic drain cleaners and some medicines in the wastewater weaken the bacteria. Decomposition slows down, sludge builds up and putrefaction produces hydrogen sulphide with its typical smell. Overloading when you have guests or irregular use at a holiday home has a similar effect.
What helps
Regular dosing of bacteria and enzymes replenishes the weakened microflora. Dose the product in the evening so it has time to work before cleaning products are used in the morning. Limit aggressive chemicals and keep an eye on the sludge level.
What bacteria won't solve
A biological product will not replace sludge removal or the repair of a technical fault. A clogged or waterlogged soakaway needs professional assessment. Keep records of cesspool emptying, and follow the operating rules and permit conditions for small treatment plants.