)last weekend while playing a concert (fooling/messing with my M-W CC during warm-up) that the 1st, 3rd and 5th slides are all interchangeable. With the first slide in the 5th, and the cut 5th slide in the female first slide tubes, it plays in tune as a BBb! 
The cut 5th slide is longer than the 1st slide, but shorter than the 3rd slide.I only have to pull the first slide (cut 5th) maybe an inch for Eb's while in "BBb mode".....and THAT'S IT. All other slides are pulled and set for proper length when in BBb mode.
As a CC, I have to use 1&5 for low Eb and 1&3 for bottom-line G. And lip a couple notes. As a BBb, I pull 1st a bit for Eb's and do light lipping for a couple other notes. That's it.
And there IS a slight difference in tone. As an 'open' CC, the tuba is slightly louder, punchier and more articulated. As a BBb, the tuba has a slightly smoother, darker quality and legato/slurred passages are, well, .....smoother and easier.
Great fun!
