That just means you'll be taking a DOT-regulated test. The testing process is regulated by the US Department of Transportation. With DOT-regulated testing, there are regulations and protocols that must be adhered to by all individuals in participation. The regulations themselves are found here: Procedures for Transportation Workplace Drug and Alcohol Testing Programs | Department of Transportation

They split my void into two vials..
This is mandatory on all DOT specimen collections. DOT requires only 45ml of urine sample. The sample is then split 30/15 (into bottle A and bottle B) and both are sent off to a lab. Bottle A gets analyzed while bottle B is put into storage. If bottle A is confirmed positive for a particular drug(s), and the donor decides to mount a challenge to the results, then bottle B gets tested.

Edit: Since youve just pointed out that your test was DOT, here is the regulation outlining what an employer is to do when s/he receives a "diluted" result:
http://www.dot.gov/odapc/part40/40_197
Burnt Toast Reviewed by Burnt Toast on . test is tomorrow.. what do yall think???? Ok, here's the skinny.. I haven't smoked a thing since September 16th. I have been clean for 47 days. Before then I barely smoked a bowl a day for maybe 6-7 months. I have taken numerous home tests (10-12 of them), with cutoff levels of 50ng.. All of which I have passed, with several of them being first voids of the day. I have a pre-employment urine test tomorrow. I weigh 110 lbs with very high metabolism. My greatest fear is that the lab test is different from the home tests.. Although Rating: 5