have seen a couple of posts where they have detected the synthetic urine. Since this is a preemployment test only, are the dilution thresholds less, and is that type of test less likely to uncover the synthetic urine?
"Non-human" urine samples are ruled when the creatinine level is less than 2 mg/dL. As long as the synthetic is from a reputable manufacturer and is a current batch thats been stored properly (ie no direct sunlight), it will pass the validity checks.
The synthetic can be tested at home with an adulteration test strip to ensure that the creatinine, specific gravity, and pH are all within acceptable ranges.

For all validity checks, a "diluted" sample is ruled when the creatinine level is between 2 - 20 mg/dL and the specific gravity is between 1.0010 - 1.0030, as outlined in the criteria established by the United States Dept of Health & Human Services (DHHS).