How can you pass a drug test within days of smoking marijuana?

You probably can't. Your best bet is to smuggle in someone else's urine and try to switch it. Barring that, drink lots of water, and don't give your first urine of the day. All the products you see advertised to beat drug tests are currently ineffective. A few of them did work at some point, but the tests have been changed and can detect attempts to cheat.