1. Park the truck on a level surface and apply the parking brake.
2. Locate the air tanks. They are usually located under the truck, near the rear axle.
3. Find the drain valves on the air tanks. They are usually small, round valves with a petcock or lever.
4. Open the drain valves. Allow all of the air to drain out of the tanks.
5. Close the drain valves.
6. Start the truck and let it run for a few minutes. This will help to refill the air tanks.
