Question All air tanks must include: Answers A drain valve. A lock. A trap door. A warning sticker. Explanation Air brake system tanks must contain drain valves. These valves are used to drain accumulated oil and water from the tanks and may be either manually or automatically operated. Take a FREE Practice Test Now This questions appears in the following tests: Alabama Air Brakes , District Of Columbia Air Brakes , Florida Air Brakes , Massachusetts Air Brakes , Mississippi Air Brakes , New Jersey Air Brakes ,