Depends on the test. If they are doing a hair follicle test you are pretty much screwed if you have touched anything for 30 day "I have heard longer" hair follicle will give them your complete DNA.

As to a piss test there are things like dyaretic "not sure I spelled the right you can take. If you take them drink tons of water. They are used to flush out extra water. The THC goes into your fat cells. So, you want to flush them out with water and the dyartics. You can buy them at wal-mart, gnc etc. Make sure you pee several times the day of the test before. Never give them the first pee of the morning because that will be your strongest. Try to pee just before you walk into the DR office. Then tell them you need a glass of water to help you pee. Drink a few glass of water. Since you just drained you blatter a few mins before this will make everything you pee for the DR fresh "the water you drank while at the dr. When you first pee into the cup do not use the first amount that comes out. Try to pee that first part into the restroom. Then us the last part for your test.

If you have several days before your test start the dyratics and water right away. The more water you drink the more you will flush