The above conjectural drawing is a reconstruction of a portable Greek Fire
siphon from a number of written descriptions plus highly stylized
illustrations in Byzantine and Islamic military manuals. An airtight
copper "box" (tank) containing inflammable liquid is mounted
above a hand-held siphon.
Reference:
D. Nicolle, et al, "Medieval Siege Weapons (2)," New Vanguard 69, Osprey, Oxford, UK, 2003
Unfortunately, the very worn Arabic inscription on the rear of the portion of the Islamic Gun (1) has yet to be interpreted. The massive late medieval iron arrow (2) found in the citadel of Damascus and now in the Musee del' Armee in Paris was probably fired from such a gun.
Reference: D. Nicolle et al, "Medieval Siege Weapons (2)," New Vanguard 69, Osprey, page 45