I wonder if anyone has ever made 3 simple tests in the laboratory, picking the first, middle and last stream and checking which of them contains what. It might be that the traditional recommendation of drinking only the mid-stream is there exactly to avoid re-drinking any toxins. At least this is what I'm prone to believe. Maybe you could make such a test yourself, while doing iodo-supplementation? in case you do, please report.
re: hypothiroidism, I must say that UT has easily cured mine. I began doing UT again last month after really long time I hadn't. I checked the basal temperature at day 10 and it was stable at 36.1, now it is stable at 36.7. Fatigue is gone, and I'm losing weight without major changes of my diet. I drink mid-stream all day long until sunset - after that it wouldn't make me sleep so I discontinue it.