A drainage system for use with a slack adjuster for a railway brake rigging. The drainage system allows fluid and other contaminants to drain from the slack adjuster to prevent the fluid and contaminants from accumulating within the slack adjuster, contacting an operating area of the slack adjuster, and interfering with the operation of the slack adjuster. The slack adjuster includes a main housing portion, a cone nut housing portion enclosing a critical operating area of the slack adjuster, and an overtravel housing portion. The drainage system includes at least one aperture extending through a sidewall portion of the overtravel housing portion. The at least one aperture is configured to allow fluid and/or contaminants to drain there through to reduce exposure of the critical operating area to fluid and/or contaminants. A plug and/or patch can be provided to sealingly and/or removably engage the at least one aperture.