I found an old solo I remember playing during my trumpet days, "Cherry Pink (and Apple Blossom White)" music by Marcel Louiguy. I could get a Pitch Fall fairly well on trumpet but it doesn't seem to work as well on euphonium for me. I tried 'half-valving' different valves and it seems from 'Bb' (TC 'C') the 3rd Valve works best but still not great. I watched Dave's excellent video on "How to Do a Glissando / Smear" and this is similar to the technique I was trying. Maybe a conical bore instrument is different?

Here's a good example on trumpet:

"Cherry Pink" - Andrea Giuffredi
https://www.youtube.com/watch?v=3HctkKKPE6A

Some years ago I played "Blue Moon" (Rodgers/Hart) with a band and couldn't bend the pitch too well from 'F' (TC- 'G'). But bumping the 4th valve worked well. Since I didn't need the 4th valve in that piece I pulled out the 4th valve slide pretty far to get a decent affect.