How to do it

If needles and syringes are going to be reused, they should be flushed with cold water first and then cleaned properly. Flushing first with boiling water can cause clotting of blood and the formation of a protective 'skin' over any droplets of blood in the needle or syringe. Viruses and bacteria can then live, unharmed, in this protected, warm, moist droplet.

• Draw COLD water (sterile or cool, boiled water is best; otherwise tap water or water from a new bottle) into the syringe and then flush it out (down the sink or into a different cup). Repeat this until no more blood is seen.

Then do this twice:

• Slowly draw household bleach into the syringe – over 30 seconds or more. Shake or tap the syringe as this dislodges particles and thoroughly mixes the disinfectant with material in the syringe. Flush it out (into the sink or into a different cup).

Then do this twice:

• Draw up COLD water, shake or tap the syringe and flush it out into the sink or a different cup. [ref] [ref]  

If an IDU ever reuses injecting equipment, it is advised they practise this technique so they can do it without making any mistakes.