Why Does a Septic Tank Smell?
Odour is a symptom with a small number of likely causes, and where you smell it narrows the list quickly.
Septic gas is produced by normal biological activity. In a working system it vents above the roofline and disperses. You notice it when a vent is blocked or badly located, when a trap has dried out and stopped sealing, or when effluent is reaching places it should not.
Location is the best diagnostic. Indoors points to plumbing. At the tank points to lids, seals or venting. Across the field points to surfacing effluent or an under-performing treatment stage.
Indoor odour
- Dried-out gully traps or unused floor wastes
- Failed toilet or waste pipe seals
- Blocked or undersized vent pipe
Outdoor odour
- Cracked or poorly seated tank lids
- Tank overdue for emptying
- Aerator failure on a treatment system
- Effluent surfacing on the disposal field
Frequently asked questions
- Will additives stop the smell?
- They treat the symptom at best. Find the cause — a blocked vent, a full tank or a failing field will not be fixed by a bottle of bacteria.
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