It was a jug (conception of Philon of Byzantium) from which water, wine or watered-wine, depending on the will of cupbearer, was poured automatically.
It consisted of a vertical diaphragm that separated the jug into the compartments of water and wine and the outlet fluid pipes which, however, were found one inside the other so that outside the jug they appeared as one. The jug had an airtight lid which made it impossible for the fluids to flow at its inversion because of the vacuum that was created by the inability to substitute the outlet fluids with air. Two tubes began in the middle of the jug (the one communicated with the water compartment and the other with the wine compartment) and reached the neck so that they formed its handle. At the sides of the tubes there were air holes which the cupbearer covered with his finger. With the combinational disclosure of the air hole of the water compartment, wine compartment or even the two simultaneously, the cupbearer allowed the incoming air into the corresponding compartments and the flow of water, wine or watered-wine according to the wish of the visitor.