How often should a septic tank be cleaned?
For a normal household tank, every two to three years is the usual answer. But the number of people using it matters more than the calendar does, and there are a few things that shorten the interval considerably.
What shortens the interval
More people in the house
The single biggest factor. A tank built for a family of four and used by eight will fill in roughly half the time.
A smaller tank
Older houses often have smaller tanks than modern ones. Small tank plus large family is the fastest combination to fill.
Heavy water use
A washing machine in daily use, or a bathroom used by many people, sends far more water through than the tank was designed for.
A soak pit that has stopped absorbing
If the pit cannot take the liquid away, the tank effectively becomes smaller and fills much faster than it should.
Commercial use
Shops, lodges, hostels and canteens often need emptying once or twice a year rather than once every few years.
Non-degradable waste going in
Cloth, plastic and sanitary items do not break down. They sit at the bottom and take up space permanently.
A reasonable schedule
- Small family, normal-sized tank — every 3 years
- Large family or small tank — every 1 to 2 years
- Shop, lodge, hostel or canteen — every 6 to 12 months
- Soak pit cleared — whenever drainage slows, with the tank
- Any tank showing warning signs — immediately, whatever the date
Do not wait for the tank to tell you
The cheapest cleaning is one done on a schedule, when the tank is accessible and the sludge is still soft. The most expensive is one done the week after sewage came back up into the bathroom.
If you cannot remember when it was last emptied, assume it is due.
Check the warning signs firstCommon questions
Is there a fixed number of years?
No. Two to three years is the usual range for a household tank, but the real answer depends on how many people use it and how big it is.
Does adding chemicals or powder mean I can wait longer?
Not meaningfully. Powders and bio additives may help with smell, but solids still build up at the bottom and still have to be physically removed by tanker.
We are a shop or lodge. Is it different?
Yes, usually much shorter. Commercial tanks on continuous use often need emptying once or twice a year.
What happens if we leave it too long?
Sludge hardens and the soak pit takes damage from being permanently flooded. Both make the eventual job harder and more expensive than a routine cleaning.
Not sure when yours was last done?
Call and tell us where you are. You get a price on the phone, before the tanker leaves.