The "Wetline" rule for cargo tanks of flammable liquid:
Correct. Wetline regulations restrict residual flammable liquid in cargo-tank product piping during transportation, due to ignition risk if a piping line is breached.
CDL Practice Question #290
Category: Hazmat
Why this question matters
This question is one of 68 in our Hazmat 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.