This is risky, but I’ve pbumed drug tests this way:

Right before you go to take your test, get a friend who is clean to **** in a cup for you (make sure the friend is the same sex as you). Funnel the **** into a small container. A sample size bottle of mouthwash works well (be sure to rinse it thoroughly). Buy a thermometer if you don’t have one. Run some hot water from the tap into a cup. Put the thermometer inside the container with the urine, and immerse the container of urine into the hot bath of water. Bring the temperature of the pee up to about 104. (If you have to drive a while to the testing site, it’s best to do this in a near-by public restroom.) Put the container of urine between your legs, as close to your body as possible. Wear tight fitting underwear and tape it to your body if necessary. I’m a girl, so I’m not sure how well this works for guys since your testicles are kept at a lower temperature than the rest of your body – maybe keep it around your taint (inside your bum would be ideal lol). Alternatively, you could try keeping it in your armpit. They’re going to make you wait there about 20 minutes before they let you go to ****. So while you’re sitting there, hug it close to your body. Bring your thermometer with you. When you go into the bathroom, pour the **** into the cup, and take the temperature. They will check it for body temperature. If it’s too cold, add a little hot water from the sink to bring the temperature up (98.6 F). Don’t make it too hot, because that will be suspicious. **** into the toilet for effect. There’s a lot that can go wrong with this, but it’s worked for me.

I’ve heard they also test for common detox products, so I’ve never taken the risk with those. Another option would be to start drinking a ton of water now, and exercise a lot. You can buy a home drug testing kit at any of the chain drug stores (like Walgreens, CVS, etc). Test yourself right before you go and if you’re positive, try to put off the test.

Good luck.

edit: If you don’t know anyone with clean urine, you can buy powdered urine online that you mix with water. If you can’t get overnight shipping, check your local head shops, maybe they have some.