A conventional septic tank should be cleaned out every three to five years. If you have or can borrow a “sludge judge”, you can use this tool annually to know exactly how much solids capacity you have left. Then, you can plan your next cleanout instead of having an emergency situation where you are trying to hire a pumper for an evening or on a weekend. If you are fortunate in hiring that “after hours” pumper, the price will undoubtedly be higher.
An aerobic treatment unit typically needs to be cleaned out less often because the solids will break down much quicker. However, some aerobic units are small. They only have 300-800 gallons of capacity. In this case, these smaller units might need to be cleaned out every two or three years. The larger concrete aerobic treatment units will need to be cleaned out approximately every ten years.
All the information above gets skewed if you abuse your septic system by hydraulically or organically overloading it. Or, perhaps, by just flushing too many non-degradable items down the toilet.
Whether you have your septic tank pumped out every 3-4 years or wait until you have an issue just remember; A Royal Flush Beats a Full House!