Used with 3/5/6 gallon glass carboys. A really easy to use tool; simply put the racking tube through the center tube, place the cap on the carboy, then blow into the other tube to begin a siphon. May also use as a blow off tube by attaching some 2/8" siphoning tube to the side tube and then run the siphon tube into a bucket/jug of sanitized water/solution.