The purpose of flushing at least twice with sterile water is to flush out all the blood in the first instance and all the bleach solution in the second. Sodium hypochlorite is available as crystals and has to be dissolved. Please understand that this is not a substitute for using a sterile disposable syringe but merely to point out that the HIV virus is fragile and easy to kill. In any case it was not recommended for blood collection.
Generally one should aim at having between 500 and 1000 parts per million of free chlorine in the syringe which has been cleaned of blood. (in other words a syringe that has been rinsed to appear free of blood, should be filled with a 1 in 100 concentration of household bleach).