Green’s Dictionary of Slang

untie v.

(drugs) to remove the tourniquet – a belt, a shoelace – used to isolate a vein for injecting narcotics.

[US] ‘Honky-Tonk Bud’ in D. Wepman et al. Life (1976) 56: The stud untied, the hipcat sighed, / ‘Like, baby, I’m really high.’.
[US]N. Heard House of Slammers 88: The dude untied and Honky sighed / And said: ‘Dig, man, I’m high.’.

In phrases

untie the frog (v.)

(Aus.) to leave.

[US]Hartford Courant (CT) sect. D 5 Sept. 27/4: G’Day from Down Under [...] Untie the Frog — leave, depart.