Overflow Tank question

[Archrms]

Ernie: That is why I differentiated between the black over-flow canister and the expansion tank in my original post.

Tim: Thanks for the input. I don't fill the expansion tank to full, however, it is possible it may have been slightly over-filled, and if the overflow tank was full already, it would have spewed out as it did. The valve at the bottom moves 90º open/close to drain the overflow tank, but the entire assembly rotates 360º. If is is press fit as you noted and not screwed in, it would explain the rotation.