Green’s Dictionary of Slang

(UK drugs) the act of drawing blood into the syringe when injecting a narcotic.

1967		Glatt et al. Drug Scene in Great Britain 116: Flushing – draw up and re-inject blood.
1975		cited in Spears Sl. and Jargon of Drugs and Drink (1986).
1989		J. Morton Lowspeak.