MyJoey: My advice is to take advantage of the shock value on your son to use as influence to get him to agree to go back into the rehab or sober living housing or something. If you just sit on this, it is VERY possible that in a few months you and your son will be back to square one.
Taking away his "stuff," deciding to give back his "stuff," buying those expensive drug testing kits and making him pee in a cup while you monitor, making him strip down are all temporary answers. You, your son, and your family cannot live like that on a regular basis. It is just too stressful. If you son needs that kind of monitoring then he needs to be in sober housing or perhaps back in rehabilitation or whatever his counselor at the drug rehabilitation suggested back when your son was in there. (Except, if the drug rehabilitation counselor suggested your son live at home with you, I would say forget that advice.)
Just my take on it. Every situation is different and has its own particular challenges. So take what you need and leave the rest.
Keep coming back.