I've taken many a drug test, and irresponsibly not abstained prior to drug tests many a time. I use a similar method to Parshvik Chintan, although I don't use it as a temporary window of clean urine. Stop this regimen with 24 hours left before test.
Lead up to to the test
Vitamins- B vitamins and Biotin for fat metabolism, Vitamin C 1000 mg, 4 cranberry pills every 12 hrs
Water- Drink 1.5-2 gallons of water throughout the day
Drink a cup of green tea 3 times daily
Eat a high fiber/low fat diet, THC is passed primarily through stool, low fat diet combined with exercise will promote burning of fat cells where THC is soluble
Exercise
Sweat
24 hours remaining
Eat a high fat diet as to deter the burning of fat cells and release of any remaining THC
Do as little exercise as possible
Discontinue vitamin regimen
Discontinue water regimen with 12 hours remaining
Wake up early before your test and urinate a few times. The first Urination in the morning is dirty dirty.
Every time I give a sample, I start the stream in the toilet till about 1/3 through, fill sample with the next 1/3 and put the last 1/3 back in the toilet.
In highschool I used this method with weekly drug tests with success, high intake of marijuana.
I had to use it again at the start of probation recently as well, also with great success, but hardly any intake at all.
Edit: Also, if you are going to flush/dilute your sample, eat some red meat before to increase creatine levels that are lowered by flushing and detectable by the testers.