So heres the deal. THC is usually out of your system in a day, however THC metabolite is the thing that stays and is tested for. The detox kits sometimes work, but it will only mask the THC metabolite for a certain window of time.
Excersise works, but you want to stop excersising 2 days before you're test, because the excersise gets the THC metabolite into you're blood.
Drinking water helps, but if you're just pissing clear it does nothing. The only time THC metabolite will be leaving you're body is if you're piss is yellow. However if you don't have time to get totally clean, you want to mask it. Drink few glasses of water and then when you piss yellow, drink somemore. by the second or 3rd piss it should be almost clear, but keep going a few times. Youll end up pissing clear, which is just water. Everytime you piss a little water make sure to drink a glass of water to refill..... and if you need the piss to be yellow, make sure to take a few Vitamin B complex, which will give you yellow piss.. hopefully that helps a little.