The last time I got drug tested for a job, I just went to GNC and bought one of those herbal cleanse drinks. It was in the neighborhood of $50, but follow the directions and you'll pass. I smoke 1 to 2 times a day and had no problems and friends have had the same results.
But if you're going to do this, you CANNOT tell them its to pass a drug test, they will refuse to sell it to you. I've had them turn down numerous friends who are idiots. Just say you want to herbal cleanse, this is what I bought.
GNC - Herbal Supplements: Natural Cleansing & Detox: BNG Enterprises HERBAL CLEANŽ Liquid Carbo -Tropical Flavored
But honestly, if it's for surgery and they're giving you a physical, be honest with them. Doctors don't care if you smoke pot, they just don't want any unforeseen complications in surgery. And furthermore, they dont want a malpractice suit either.