Drainers are humans who attack vampires in order to drain their blood in "The Southern Vampire Mysteries". Not to be confused with Fangbangers, drainers travel in teams, single out vampires through a variety of methods, and then carefully plan their attack.
The drainers will ambush the vampires, binding them with silver chains. They then proceed to drain the blood into vials. The strength of the blood depends on the age of the blood (the time since it has been removed from its owner), the age of the vampire from whom the blood has been removed, and the individual chemistry of the drug user.
Drainers can be found in several books in the series.