I have heard that drinking a lot of orange juice the night B4 works. Also most "head shops" sell some sort of cleaning agent that should work.
"Cleaning agents" are an overpriced form of dilution and the O/P has expressed that s/he hasnt got the money to spend.

you don't realistically think 30/40oz's 4 hours before the test would screw me do you?
Im not one for guesswork. If you really need this job, relying on guesswork is not a wise idea. Nobody knows what your "baseline" creatinine & SG levels were before drinking 30-40 oz water, so theres no telling. Only those validity test strips would give you that realistic assessment.

and what happens if that did occur?
The lab will report the result to your employer. How the emloyer will handle the result deppends on the employer. Some employers may grant a retest, particularly if theyve somehow had taken a liking to you; while other employers may only be concerned that no drug metabolites were detected in your sample.
Still theres many others that will simply move on to the next candidate for hire.