Detox drinks are overpriced bottled diluters. You can spend huge sums of money and accomplish nothing different than you can accomplish with just vitamin B2 and water.
Drinking water days before the test is no help. THC is not water soluble so you cannot wash THC out of your body with water like you can wash dirt from a vehicle. Drinking water is only helpful on the day of the U/A.

Niacin is a myth. It does nothing to rid the body of THC.

There is nothing that can permanently rid the body of THC except time and exercise.