How often should you drain the air tanks?

Air tanks should be drained every day. Most modern trucks have automatic drain valves that release water and oil periodically without driver action, but drivers should still verify these are functioning. If automatic drains are not present or have failed, drain manually by opening the petcock at the bottom of each tank. The wet tank (supply tank) collects the most water and is the most important to drain. In humid weather or after long compressor cycles, more water accumulates. In freezing weather, undrained water can freeze in the lines or valves and block air flow, causing brake failures. Allowing water to accumulate also corrodes tanks and components over time.