Fake urine is definitely the most for sure way, however it's not always possible to get. Maybe you can't wait for shipping or you don't have a smoke shop or what have you.
In that case, here's what you do. Don't use that detox crap, they usually don't work. Note how almost all detox drinks say to drink it with lots and lots of water. If a detox drink EVER works, it's because you drank a ton of water with it. These companies make tons of money off of panicked people who desperately need this job enough to spend $20-40 bucks on their bogus product. The way that these tests work is they test the amount of THC that exists in the urine sample, so if your urine sample has little to no THC in it then you'll pass. So how do you do that? Well have you ever drank so much water that your pee came out completely clear? And on the opposite end, have you ever realized how your pee is the darkest in the morning? This is because when you pee in the morning, you're getting rid of all the fluids that you not only didn't expel the day before, but also while you were sleeping. Make sure you pee first thing before your drug test, then keep drinking plenty of water. Keep drinking until you pee clear, when your pee is clear it is more "pure" in the sense that there won't be much THC in your urine sample and it will likely not be detected.
Of course there's the problem of clear urine raising red flags. So what you do when your pee first starts turning clear, continue to drink water and swallow a couple of B12 vitamin pills. The B12 just so happens to make urine more yellow, so even if your urine is coming out "clear" it will be colored yellow and it will likely not fail the drug test due to it not having as much THC in it, that's why you don't take the first piss of the morning for your drug test, you'll get nailed for sure. If you do this with enough time before the test your body will be able to provide it's own "fake" urine
Hope this helped.