Since you are a once a month smoker and its been 30 days you should be ok. The home tests are highly accurate up to 98%. The test will indicate whether or not you have 50 ng/ml of thc metabolites in your urine. If you are 50 or above you are positive, 49.99 or below and you are negative. 50ng/ml is usually used since its the standard cutoff. Most tests are pass/fail using the 50 ng/ml cutoff. If you fail then to confirm the lab will run a gc/ms test which is more accurate and will check for a specific thc metabolite at usually a 15ng/ml cutoff. For safety you may still want to drink 40 oz of gatorade prior to your ua and void at least two-three times before giving your sample. Good Luck.

P.S. The intensity of the T line means nothing, a line is a line.