Which of the following could lead to a septic-tank failure?

The correct response highlights the importance of regular maintenance and the consequences of neglect in a septic system. A lack of routine cleaning can lead to the buildup of solids in the tank, which prevents the proper function of the system. Over time, these solids can overflow into the drain field, causing blockages and ultimately leading to system failure.

Additionally, leaking fixtures contribute to an overload of the septic system, introducing excess water that it may not be able to adequately process. This influx can saturate the soil and disrupt the natural biological processes that break down waste. Therefore, neglecting regular maintenance and failing to address issues such as leaking fixtures creates conditions ripe for septic system failure. This response underscores the necessity for consistent upkeep to ensure the longevity and effectiveness of a septic system. Other options, such as regular inspections and properly sized components, are aligned with preventive measures that help maintain the system, while efficient absorption systems reflect good design, both of which are less likely to contribute to a failure scenario.