Quote Originally Posted by Riddle62
...please refrain from posting here again, as this forums advice can have major implications in peoples lives.
Missed the edit window.
I haven't seen any scientific evidence other than word of mouth in this thread. The only advice I see here is drink water and take vitamins. This is straight from the CA NORML website.

"WASH YOURSELF OUT: The general strategy for passing urine tests is to increase your fluid intake and urine flow so as to dilute the concentration of drugs in the sample below the threshold of detection. An hour or two before the test, you should fill your bladder with fluids - as much as you can drink. Water is fine - contrary to popular rumor, there is NO evidence that goldenseal, vinegar, niacin, or vitamin C help. However, high-dosage aspirin may reduce the sensitivity of the EMIT urine test for pot (only). Many people wash themselves out for several days in advance by drinking a lot and exercising, but there is no reason to think this is useful. In no case should you give your first urine of the morning, since drug metabolites tend to build up during your sleep.

While you're loading up on water before the test, you may also want to take a large dose (50-100 milligrams) of vitamin B-2, available in B-complex multivitamins. The purpose of this is to color your urine yellow, since otherwise you are likely to produce clear, watery urine, which makes some collectors suspicious (contrary to rumor, vitamin C won't help). In rare instances, some labs will reject a sample for being too watery; in this case, however, they will typically give you a second chance. Wait until your test results have been confirmed before indulging in compromising behavior.

You can boost your fluid output by taking diuretics, which stimulate urination. Weak diuretics include coffee, cranberry juice, certain health food products and over-the-counter pills for pre-menstrual water retention.

If you're taking the test on very short notice, you may wish to resort to more potent diuretics, which are widely prescribed to treat high blood pressure. Although strong diuretics, such as furosemide (Lasix®), are available only on prescription in the U.S., they can be had over-the-counter in Mexico and other foreign countries. Beware that they can be dangerous for certain persons, such as diabetics or pregnant women, and can cause problems if taken over extended periods. Diuretics can be detected in urine, but are rarely checked except for athletes. The following regime has been suggested by a former army drug testing officer (Robert Freeman, "How to 'Beat' a Drug Test," High Times, Aug. 1988): Take an 80-milligram dose of Lasix; take a hefty drink of water; piss two or three times, then take the test. If you're lucky and didn't smoke too much pot, a good washout may get you past a test on a couple days' notice. However, regular smokers should allow at least a week or two if at all possible. "
Drug Testing | California NORML