Dark metallic gray tube: Is it a LEGO?
Sounds like 'Hose, Rigid 3mm D. 16L / 12.8cm' in Pearl Dark Grey. Super Battle Droids are also in Metal Blue but none of the hoses exists in this color. Also note that the linked hose also exists in other sizes too and that the exact piece you have had might have been cut.

Note that colors mentioned refer to Bricklink's color names, LEGO company's official color names are different.