Designed for rapid mass treatment of cattle, the Automatic Backpack Drencher allows one to treat without having to stop and refill the drench gun-a task that otherwise requires both hands. The dosage barrel refills automatically from a 21/2- or 3-liter poly backpack container that comes with adjustable straps. Most units feature: aluminum alloy handle and lever; graduated transparent barrel; dripless stainless steel nozzle; and springless valve inside the plunger. All provide for exact dosage delivery adjustable from 21/2 to 20 ml or 5 to 50 ml, depending on the particular model.