My system for passing a piss test, and trust me I've passed a lot of the mothers:
1.) A day before the test, start drinking A LOT of water and pissing, pissing, pissing.
2.) Cranberry juice or other acidic juices helps too. Drink a lot of these and still piss often.
3.) Starting the DAY OF THE TEST, do the following!!! - Wake up early and piss hardy, start drinking a LOT of water immedeately. Piss, piss, piss my son. This is the true answer to passing that test. Get all that dirty piss out and replace it with clean ol' water. Remember the first piss of the day is the dirtiest!
4.) About three hours before the test, drink 1/2 cup vinegar. Some people will deny that this works but hell I've never showed positive and I test all the time. I heard it has something to do with the metabolite release of the kidneys, and seriously who gives if it tastes like shit as long as you pass! Take a vitamin C tab or two to recolor all that water that is now passing as ur weewee hoohoo.
5.) Take the cup from the watcher and piss like a true master, make sure to splash that piss all over the place so they don't try to say you cheated. Piss until the cup brims and the floor is soaked and your shoes are flooded. Hand it over to THE MAN and watch his grin twist when you pass. It can be done! I'm living proof!!