The faintnest of the line has nothing to do with thc levels. A line is a line, even straight water will show a faint line a lot of times. They evidently don't really care about the UA tests, which is good, its just for show.
If you've been a regular smoker you may not be able to pass with just dillution. If you smoke a couple times a week you probably can. Morning of the UA follow the dillution sticky, use gatorade instead of water and don't bother with the aspirin.