You should drain the air tanks:
Correct. Drain all air tanks at the end of each working day to remove water and compressor oil that has condensed in the tanks.
CDL Practice Question #151
Category: Air Brakes
Why this question matters
This question is one of 71 in our Air Brakes bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.