2024 CO CDL Practice Test: Tank - Test 2 Based on 2024 CO CDL Handbook 8. How often should trailer air tanks be drained? A Every day. B Only during warm weather. C Every two months. D Once a year. Next More 8/28 Progress 0 Errors Restart Next Next Tank - Test 2 Back to Test List Tank - Test Tank - Test 3 Challenge Library 12 More CO CDL Practice Tests 31 Tank - Test 3 32 Tank - Test 4 33 Tank - Test 5 34 Air Brakes - Test 35 All - Test 36 All - Test 2 37 All - Test 3 38 Tank and Hazmat - Test 39 Tank and Hazmat - Test 2 40 Class C - Test