The carboy brush is a special "L-shaped" brush that is used to clean out glass carboys. It is very similar to a bottle brush, except that it is a little bit longer, and shaped like a "L". The "L-shape" allows for easy cleaning of the carboy sides. It is important to keep the carboy brush as clean as possible, thoroughly rinsing and washing after each use. (Also hang to dry).
It is suggested that you rinse with sodium metabisulfate before and after each use.