I'm sorry for the delay - I was having weather related internet problems.Yes, I have had considerable experience with these tests. I am a Medical Review Officer (MRO) - a physician with specialized training and certification in the interpretation of drug tests required by the DOT and other federal agency drug testing programs. I have worked with a number of local employers and universities to establish and supervise their drug testing programs.The detection period for marijuana is much shorter than most internet references would seem to suggest. Even NORML - a strong opponent of drug testing references this fact on their website:http://norml.org/news/2006/02/23/marijuana-detection-time-shorter-than-previously-assumedDetection beyond 30 days is really rare. Here is a link to the actual paper published in Drug Court Review (the article starts on page 23 of the journal)http://www.ndci.org/sites/default/files/ndci/DCRV5_1.pdfHere is a reference from a laboratory that offers the "zero tolerance" testing with thresholds of 20 ng/ml for the screening and 5 ng/ml for confirmation. They advertise an expected detection period of "up to 10 days".http://www.aegislabs.com/About_Aegis/Zero-Tolerance_Drug_Testing/Period_of_Detection_TableAnother excellent source is this article from the Mayo Clinic. You will see that the only cases were you may see detection as long as those reported on those websites is with heavy daily use.http://download.journals.elsevierhealth.com/pdfs/journals/0025-6196/PIIS0025619611611208.pdfI believe the reason many sites repeat the myth of 30+ days for detection is to scare individuals into buying their worthless/fraudulent products that are promoted to "clean", "flush" or "mask" drugs to allow someone to pass a test. If you are convinced that the detection period really is 30 days and you pass a test in less than 30 days after using their product - you are of course convinced (and will tell all your friends) how effective they are. In reality, the reason you passed the test has nothing to do with their product.
In medicine, I try to avoid two words; "always" and "never", but in this case, you are more than 3 weeks from a single low level use, I really don't see any reason to be concerned.