On a probation drug test is a faint line a passing line?

Yes, a faint line is considered negative. Most packages state that in the instructions. Standard EMIT urine tests (test strips) do not determine how much metabolites are in your system. They only tell you if they are present or not present. They have a 50 ng/ml threshold. If the testing site determines that the sample may be diluted, or if you test positive (no line at all), then they will send a sample to a lab for a more intensive test called the GC/MS test, which generally has a cutoff of only 15 ng/ml. That means that even if you test negative on the EMIT test, you could still test positive with the GC/MS lab test.

Here's a link with more information:

http://www.craigmedical.com/drug_test_faq.htm