What is the best way to fake a piss test at a doctor's office?

I'm still in high school so I'm not old enough to consent to medical treatments and my whole family knows that I do drugs so when I go to the doctor for whatever reason, my parents will tell the doctor that he does drugs so they can test for it. They don't say specifically which drug but they always test for weed. So I've failed every drug test for the past three years and have to go in for my physical before the school year starts tomorrow and I have a doctor's appointment at 1:30 so I want to know the best way to pass the test. I don't have any synthetic pee and I'm not hydrated enough to dilute the THC to the point that I can pass. My doctor's office is a small one so I'm sure the doctor or his secretary will hear if I try to sneak synthetic pee into the bathroom so I'm not sure what to do. I've heard that if you eat poppy seeds, it can trigger the test for opiates because they have similar compounds or something but I'm not sure what foods would be good for my situation or any other methods. I'd appreciate any advice because I'm sure my doctor's going to be pissed if I fail again because he already ran out of patience the last time this happened.