If the lavatory sign is lifted, what is one action that can be performed?

When the lavatory sign is lifted, it indicates that the lavatory is available for use. The primary action that can be performed in this situation involves unlocking the toilet latch. This step is essential because it allows passengers or crew members to access the lavatory.

The other options may be tasks related to lavatory maintenance or operations but are not actions that are directly associated with the immediate consequence of lifting the sign. For instance, checking the water supply or ensuring the toilet is clean are more about the upkeep and readiness of the lavatory, which would typically be done prior to opening the lavatory for use. Activating the flushing mechanism is also an action related to the functioning of the lavatory but does not pertain directly to the immediate unlock action signified by lifting the sign.