An air tank without an automatic drain has a manual drain valve. How is it typically operated, and how often must the driver use it?

AAMVA CDL Manual, Section 5, subsection 5.1.4 (p. 5-1), 'Air Tank Drains'

Drivers, not mechanics, are typically responsible for this basic daily maintenance task, and skipping it is a common cause of moisture-related brake problems. The exam checks that you know this is an end-of-day driver responsibility, not something that happens automatically on every vehicle.