What does it indicate if the LAVS INOP indicator illuminates in the rear CSA panel?

When the LAVS INOP indicator illuminates in the rear CSA panel, it serves as an alert regarding the lavatory system. Specifically, this indicator notifies the crew that the lavatory system is not operational. Therefore, the correct answer aligns with the context of system functionality rather than the state of the tank's contents.

The illumination of the LAVS INOP indicator signals that there might be a malfunction or failure in the lavatory system, which can lead to an inoperable system. It does not indicate that the tank is full or nearly empty, nor does it verify that the lavatory system is indeed functioning. This situation typically requires immediate attention to ensure the maintenance and operability of the lavatory facilities onboard.