Factors that change the interval
Tank size, number of occupants, garbage-disposal use, leaks, high water use, and what enters the system all matter.
Use records, not memory alone
Keep dates, invoices, inspection notes, tank location and access information. A provider can use that history when discussing the next interval.
Do not wait for failure
A backup is not a maintenance schedule. Address slow drainage, odors, alarms, surfacing wastewater or unexplained wet areas promptly.