Common septic tank pumping frequency mistakes
Failure to pump the septic tank frequently enough: leading to an early drainfield failure and costly repairs
Pumping or cleaning the septic tank too frequently, wasting money (though you're wasting a lot less money than the cost of a new drainfield.
Some septic pumping contractors and some other "experts" give a fixed rule of thumb that serves their own interest, such as "pump your septic tank every year" or "pump your septic tank every two years".
Contractors may give this advice without first having actually considered any information about the septic system capacity, level of usage, age, or other conditions. It's a great example of "OPM" or "other people's money" - spending someone else's money to reduce your risk that they'll complain that your advice wasn't safe enough.
Pumping the septic tank with the fantasy that doing so will "fix" a clogged or failed drainfield. All you really gain is a few days of toilet flushing before the tank has re-filled.
Actually inspecting the septic system, diagnosing any problems or failures, and inspecting conditions inside the septic tank will tell us whether the tank is being pumped at the correct frequency.
The removal of septic waste by cleaning the septic tank is a critical step in septic system care as it extends the life of the septic field. Even if you don't care how septic systems work you need to know when to clean the septic tank by pumping out septic waste.