OK, sounds like you have a few misconceptions, first of all, drinking all that water every day isn't really doing anything (besides keeping you well-hydrated). Secondly, while Urine Luck would probably work, its really easy for labs to test to see if you've used it, so if you want to risk it go ahead, but I wouldn't.

But none of that matters, what matters is whether you are free of THC metabolites. The 18th was 5 days ago. How often did you smoke BEFORE that time?

Note about the water-drinking: What I always do is drink several liters of water about 4-5 hours before my test, that's the idea with water-loading, to dilute your urine for the time you take the test.