Question If using air tanks with manually operated drains, how often should you drain the tanks? Answers Every day Once a week Once a month Once every 3,000 miles Explanation To prevent the build up of oil and water in a vehicle's air tanks, manually operated air tank drains should be used at the end of each day of driving. Take a FREE Practice Test Now This questions appears in the following tests: Texas Knowledge Test Class A , New Hampshire Knowledge Test Class B , Florida Air Brakes , Illinois Air Brakes , Utah Air Brakes , Wisconsin Air Brakes ,