Not much time for prepping. Is it a DOT test or pre employment, or something else? It makes a difference. the safest way to pass is with subbing with a synthetic urine like quickfix. Just takes a few minutes of practice to get the drill down.
If all thats available is to get clean naturally.
Start eating red meat now or take creatine tablets.
3 days before test stop exercising and change to a high fiber diet.
Morning of the UA
Drink 36 ounces of gatorade
Pee 3 or 4 times
Use your midstream urine for the collection cup.
Ive been in a Mental Health (Out Patient) For Drug Rehabilitation/Mental Illness and I can tell you this now. I could smoke once or twice a week and get by.
I drank about 1 gallon a day. Im also on Medication that makes me go pee about 15-18 times a day so that helped. I would also advise like weed420 said, Red Meat and Creatine. You want to get the high protein to kick your Kidney/Livers ass. Then the morning of, Make sure to drink about 5-7 Glasses of water. Then Pee atleast once or twice before going to the pee test. Result = Diluted pee and a much lower micro-part per gram (However the measure it). Its how I did it, Worked very well.
*Also Drink lots of PURE (The stuff that tastes really bad) Cranberry Juice*
^^ That will detox you like no other.