FIRST OFF.. THIS IS NOT A QUICK PASS THE NEXT DAY POST

I'll start with my stats.. male...5'8".. 205lbs.. developed belly after college / sports but still fairly athletic, average metabolism. Smoke 1 - 3 one hitters on weekdays with 3 or more bowls on the weekend (sometimes more) over the past year.
The best one I have found and have used to pass a pre-employment test is Qcarbo32 from GNC. This is formulated for detoxing before starting a diet or exercise program and contain what you need to keep your levels in the normal range.
Because I always like to be on the safe side I usually back it up with the red meat a couple days before for creatine and get my system ready the night before with drinking 32oz of water before I go to bed. Three hours before your test start with 16 oz water. About an hour later the qcarbo32, then follow by filling the bottle back up with water and drink that. After an hour, void at least 3 times and you are good to go. When you get there make sure you do not sample the beginning or end of your stream. You are good to go for up to 3 hrs. I wouldn't go any longer than that unless you haven't smoked for 20+ days or smoke much less than me.
Again, I said I am cautious so I test myself before I go and use an adulteration stick to ensure my levels are correct (some kits u can buy come with them, but I have purchased a pack of 25 online for about $25 including shipping). I have never had them be off, but if they are there are things you can do such as drink an energy drink with creatine to raise your level or gatorade to help restore specific gravity which would both giving a diluted result. (you may get a retest if it is, many people return diluted and it does not mean fail.)
Also keep a couple things in mind, the longer you lay off smoking, the better off you will be. Everyone's metabolism, body fat and the way your body processes the Qcarbo32 is different. I also know when my test will be and do have some time to plan and prepare. I have friends who smoke daily and have smoked the night before and passed with detox drinks for employment tests.
I bought two bottles (yeah, 50 a pop) and drank one Monday after not smoking for three days and it returned a negative on a first check home cup test (I like to do a test run to plan my next . My next test isn't until next week so I have some time to do the other stuff like exercise (only up until 2 days before) and eat lean non-fatty foods to get as many of the metabolites out as possible.
It has worked for me in the past and I am using it again as I do not want to run the chance of substituting or using synthetics as some tests have detected them (though just like those who have failed with qcarbo probably didn't use it right).
Sorry for the length, but wanted to cover everything.