Can't see any line in the pictures. Any line is all you need. Makes no difference how dark it is. Its always risky going the trying to get clean or the dillution route. Your body naturally fluctuates its metabolism every day so while you might show clean one day you may show up dirty a day or a week after. It really boils down to how bad you want this job. If its something that you really have to have then subbing is always the safest way to go.
Myself as an example I'm 6'1" 280lbs, it would take me probably 90 days to get reasonably clean and even then it would be risky for me to try dillution. I just always sub. A lot less stressful. I don't have to change my lifestyle because some nazi thinks I'm going to be smoking on the job. Once you sub once it becomes very easy after that. Just get the temp within range and your golden.