It will vary depending on how many people are living in a household and how much water is used when bathing, washing clothes, dishes, etc.
For and average family of 4 or 5
Roughly every 5 years.
Roughly every 5-7 years.
HOW DO YOU KNOW WHEN THE SYSTEM IS FULL AND NEEDS TO BE PUMPED?
Toilets flush slowly
Water backs up in the shower or tub
Standing water in your drain field
Water and/or sludge around the lid of the tank
Similar to conventional but...
Sprinklers may discharge dark, foul smelling water
(if clear and smelly, you may just need to add chlorine and/or have the aerator checked)
Water is dirty and thick in the pump tank - like a really thick malt.