The more I think about it he probably used it to clean his rig.. Keep looking around as you might find spoons that have been burnt on the bottom.. foil.. razors... things like that..
probably was used to liquefy the heroin too shoot it if that was his means of taking it... Congrats on your son going to detox.. I wish you both well in the future..
normal saline is used in hopitals/salt and sterile water..comes in vials and is used to flush iv's and such..or mix with medications..
Sodium Chloride is table salt.....i dont know of any abusive/addictive characteristics of the liquid form. maybe the bottle is mislabeled?