It's a highly sensitive industrial/petro-chemical plant position (I'm a chemical engineer).

Also, I did a home drug test last night and I came out clean (below 50ng).
I'll test again using my morning sample in a few days and see if that turns out clean as well.

Since I came out clean last night, I'm not too worried, since the test is not for another 6 days. I probably just drink a couple glasses of water before I give my sample.

Note: I'm going under the assumption that all pre-employment tests are looking for 50ng or higher.