EPA sets septic cleaning guidelines
The Environmental Protection Agency recommends you have your septic system inspected at least every three years by a professional and your tank pumped every three to five years. According to the National Environmental Services Center, as solids build up in a septic tank, there's less room for the liquid and thus less settling time. The accepted maximum level of solids in the tank is one-third of the liquid depth. Any more than this and the tank is overdue for pumping.