My good friend has done this several times. You can buy these over the counter they are Called AZO, they are for urinary tract infections. Take them about two days before the piss test..they clean you out completley..you will piss metallic orange. just make sure you drink lots of water. The reason you take it a few days before is because if you walk in there completley clean of everything...the drug testing facility will know something is up.
Also, 1tbl spoon of vinegar (white) mix with 1 8 oz glass of water. drink..drink water..lots of it...repeat the water and vinegar a couple of times. Take some niacin, drink more water..take you piss test. My friend got a call from an employer for a job. She had just smoked that day. she delayed the urine test until the next day. she did it and passed her test. other people i know have done the same thing.