No you didn't. Their urine was too dilute. There is no "flushing" MJ out of you. It's fat, not water soluble, so the metabolites store in your fat cells and are released very slowly. The test is actually for the byproducts of THC. There is no possible way except time to get it out of you. Every flush product is absolute garbage. The only ingredients that make those work are water (to dilute the urine) and vitamin B2 or B12 (to make the dilute urine yellow). The problem is that most lab administered tests also test for creatinine. The level of creatinine in normal urine is known. Diluted urine has diluted creatinine levels, so they know when you are "flushing" (lol). They also test for masking agents, such as nitrites. Any commercial masking agent type products is known and tested for.
The tests do not come back positive unless a certain threshold is achieved; usually 20-100 nanograms/milliliter. This is why dilution works as far as the drug metabolites themselves go; it makes the level of THC metabolites in the urine less than the threshold for a positive.
If they suspect dilution, they do one of two things, order a second test, or run the sample through an INFALLIBLE test, which not only can not be beaten (with a legit sample), it can discover the most minute amounts of anything in your urine, a mass spectrometer gas analyzer test. Any positive "stick" test is also verified using one of these machines, so the IcebergSlim's comments about how flawed these tests are are plain wrong. The cheap stick tests are flawed, but the verification process is infallible. Some employers, because of the sensitivity of the work, order MS/GA tests only. The only way to beat this test is with a false sample (someone else's pee). I believe someone here covered this method of cheating.
Usually, for a lvl 70 smoker, it takes 2-6 weeks for the metabolites in urine to fall below the threshold for the stick test. It can take over a year for everything to to be completely out of the system. It all depends on the person's metabolism, i.e. don't be a big fat chronic dope smoker.
Ironically, all the other drugs they test for flush out of your system in under a week, most in hours. All of the so-called hard drugs are gone quickly without a trace. ...except in your hair.
As far a civil liberties aspect, employer drug testing is a highly invasive, guilty until proven innocent affair. It's fucking sick, and should be banned. Unfortunately, drugs have been insanely demonized by the government and special interest groups, and most people are willing to go along with throwing away their rights.