When should you drain your air tanks?

There are two reasons to drain your air tanks. First is to drain any water out of the tank so that valves do not not rust up internally and fail as well as giving you more air capacity. The other reason is a preferred safety reason so that your parking brakes are sure to engage. When air is completely released from your brake chambers the internal spring expands and engages your parking brake, draining the tank ensures that the air is absent from the brake chambers