Yes I do believe that if you mixed clean urine with urine that has been "contaminated" it will show up in a drug test. I'm not completely positive, but even the slightest will show in the test.
Probably not, the clean stuff should of took over. Ever heard of NIACIN Tablets. They are a vitamin B12 which is actually flushes toxins out of your liver and bloodstream. I've tried everything and niacin and cranberry juice taken after the last use has worked for me for 8 years now! No joke. It's probably the only true thing that does work. You have to take 4 or 5 of them at a time but they do the trick.