I've done this five times with success, and I've helped several people pass using this method...
First off, you only need a few hours heads up to pass a urinalysis. The trick is not to "clean out", but to dilute your urine AND disguise it as the tall deal. It's very easy to do but I would highly recommend a few test runs to get your body's timing down.
Ok, a couple hours before your drop, pop a men's daily OR B-complex vitamin, a tbsp of salt (guzzle with a few oz water), and start steadily drinking water. Don't water-log yourself, just enough to make you urinate 3-4 times an hour. I'd say around 20oz every 30 mins or so, maybe more depending on your body. Make a note of how long it takes for the vitamin to make your urine bright yellow. You wanna try and time it so that you drop the 2nd or 3rd time AFTER the 1st time you urinate bright yellow.
Also, take another vitamin and tbsp of salt 30-60 mins before the drop.
WHY THIS WORKS:
The first indicator that urine is diluted is a clear color. The B vitamins cover that.
If the lab is suspicious of your urine being diluted, they'll do a specific gravity test to check the electrolytes in the urine, and the salt covers that.
No matter how much of any drugs are in your system, if your diluted, it won't show up. I've used this method with thc, morphine, addorall, and cocaine in my system and passed every time. Hope this helps!