Whenever you test yourself always use the first urination of the day when THCA concentrations would be at their highest. For more info, do an Advanced Search with the terms "testing worst case scenario".

And by doing a search with the terms "drinking water useless", you'll discover that drinking a bunch of water in the days before a U/A is of no help.

Vitamin B2 does nothing to rid the body of THC. B2 is used during dilution techniques to bring color back into the urine.

There is no product that can rid the body of THC (that includes those "5-day detox tea programs" and/or the like). The only proven way to permanently rid the body of THC is time and fat-burning exercise.