What maintenance has been performed on the septic system?

The correct answer highlights that the septic system has undergone yearly maintenance without any issues. This indicates a proactive approach to ensuring the system remains in good working condition and is regularly serviced to prevent potential problems.

Yearly maintenance is standard practice for septic systems, allowing for routine inspections, cleaning, and the opportunity to address any minor repairs before they escalate into more significant issues. This option emphasizes the importance of consistent care and the positive outcome of that maintenance approach, as indicated by the absence of issues.

The other choices reflect less typical scenarios. Bi-annual maintenance might not be necessary in all cases, while monthly check-ups could be excessive for most residential systems. The idea of complete replacement every two years suggests a severe and unusual level of neglect or systemic failure, which is rarely the case for well-maintained septic systems. Thus, the yearly maintenance without any issue stands out as the most reasonable and effective option demonstrating proper care of the septic system.