Question Air tank drains: Answers Should not be used in cold weather. Are helpful to remove water and oil from the air tanks. Are used to move air to the brakes. Explanation Compressed air in an air brake system usually has a certain amount of water and oil in it. This can harm the system if allowed to accumulate. Air tanks have drain valves to aid in removing water and oil from the compressed air. Take a FREE Practice Test Now This questions appears in the following tests: Alaska Knowledge Test Class A , California Knowledge Test Class B , New Mexico Knowledge Test Class B , Kentucky Air Brakes , Louisiana Air Brakes , Ohio Air Brakes , Oklahoma Air Brakes , South Dakota Air Brakes , Vermont Air Brakes ,