if you don't smoke you're fine.
if you do smoke, please don't waste your money on drinks. they're not guarenteed, and the same results can be obtained using aspirin, water, creatine, vit b, and some rolaids to raise your specific gravity.
all that, and the test can still come back diluted. best method is substitiution unless you'll be observed. if it's a pre-employment test, you won't be observed.
Substitution by N2---http://www.marijuana.com/420/showthread.php?t=26485
Dilution and Aspirin, The Technique---http://www.marijuana.com/420/showthread.php?t=19579&page=1&pp=10