The frequency of septic tank pump outs will vary from system to system and there is not set frequency. The Ontario Building Code requires septic tanks be pumped out when the sludge and scum measurements combined reach a measurement that is 1/3 of the operating capacity of the septic tank. During your regular service inspection, the technician will advise is the sludge and scum has reached 1/3 of the operating capacity and requires a pump out, or if they recommend the septic tank be pumped out for another reason, such as the presence of debris or an unhealthy tank environment.