A septic tank overflow occurs when wastewater can no longer properly move through the septic system. This can happen due to excessive sludge buildup, drain field problems, blockages, or system failure. When a septic tank overflows, wastewater may back up into household plumbing, surface in the yard, or create unsanitary conditions around the property. This article explains the causes of septic tank overflows and the potential damage they can create within a septic system.