The State of NH Env-Wq 1023.01 says: ” Septic tanks shall be inspected for accumulation of sludge and surface scum at a frequency sufficient to allow the tank to be pumped by a licensed septage hauler when the combined thickness of the sludge and surface scum equal 1/3 or more of the septic tank depth.”
The general rule of thumb is to pump the tank every 3 years. Any good septage hauler should be checking the sludge and surface scum levels and should be able to advise to maintain, increase or decrease the frequency of pumping.
