is it possible to overtighten a compression fitting? i found with my tubing (tygon s-50-HL) that after a while (ie a half-hour or so, while i was doing up other things) i could screw the collars down further, basically to the point that they're all more or less screwed all the way in. it wasn't easy to do mind, i used rubber gloves to get a proper grip.

been leak testing and there seem to be no problems.