I looked through both ends and can see clear daylight through both ends, so I can only conclude the panels don't have the discs they talked about. Anyway, I just came in from repiping the sytem. I have the two panels next to each other with a flexible connector tying them together at both ends. I am feeding water into one tied header and withdrawing from the tied heater at the other end. Seems to be working quite well this way.