Depending upon how accurate they want their test to be, they will have several safeguards in place that make it very difficult to use someone else's urine.
The first is they usually watch you "donate" the sample, or at the very least do NOT let you take anything in with you. Also they check the temperature to see if it is fresh. Then they go from there.
I only know about DOT testing, but they make it very difficult to substitute someone else's urine and then also screen for it at the lab. If they send you to a lab some where to collect the sample, find out if they check for picture ID. If not then have a friend that is clean go to the lab posing as yourself and donate the fresh clean urine.
Have you read the sticky on testing clean the same day you smoke? I glanced at it once and it seemed to have some good information. I really didn't pay any attention because I don't have to worry about it. I just reviewed it and most all of them swear by that method, but I know they check for specific gravity and if it is too low, kind of like doesn't have enough dissolved solids in it, then they reject it as diluted and either fail you or make you retest so I don't much think it works. Also, how is coating the lining of your stomach going to effect your urine when the urine is filtered out of the blood, not out of the stomach lining?
Here is a link for a book that comes highly recommended. I just checked and you can down load it from hxxp://www.mediafire.com/?nnciwdmn2ud. The title of the file and the book is Passing Drug Tests The Gospel of Getting Clean for UA's by Kenn A Biscranium-1.pdf
Good luck.
Great smoking.
