The siphon is filled by immersing it in liquid and stopping a small hole in the handle with one finger. Removing the finger from the hole allows the water to flow out. Although the shape is rare, it is attested over a rather extensive area from mainland Greece to Ionia.
Kefalidou, Eurydice. 2003. "A Group of Peculiar Archaic Vases." Egnatia, 7: no. B1, p. 81, figs. 10a-b.