3/8" OD siphon starter. One of the best ways to start a siphon. No more sucking on siphon hoses! For carboys, gallon jugs and pails. Requires a 5 foot piece of 5/16" ID flexible tubing (our catalog number RB02). The plunger on the racking tube starts the siphon as you push it into the long cylinder. One of our favorite products!