Well, I for one am certainly going to have to take a closer look at my plans: I've got 3 high points where air could get trapped, and only one of them is an airtrap.
I'm thinking about mounting my heatercore upside down, so that it can drain easily, and have the tubes at the bottom, instead of the top, but that doesn't solve the problem either.:shrug: and could actually make it worse!
Then I'll have 1/2" copper pipes, running up and down, to feed the power array. I think I can simply add a removeable cap on top of it.
Maybe I ought to simply weld a drain cap into the bottom tank of the heatercore.