That’s really interesting. My ‘flap tongue’ technique comes from emulating the sound of a drum playing a military type tattoo (if that’s the right expression); basically, going trt-trt-trt-trt really fast. I tried it again this aft and can easily get 240 (720 notes per minute), on the Arban exercises. However, it sounds too much like a machine gun going off rather than a musical note so you’re probably right, I should bin the idea.
Regarding tongue position, I use ‘tongue anchoring’. This it totally inadvertent; I noticed that the tip of my tongue naturally rests against the inside of my bottom lip, on all but the lowest notes. I read about tongue anchoring (or anchor tonguing or whatever it’s called) on a trumpet forum - it’s a big discussion topic amongst trumpeters, it seems. I think it’s a misnomer- the tip of the tongue is never ‘anchored’ i.e. immovable, it just finds somewhere to lay up. This does push my tongue forward though so will, I think, help with speed, as Dave suggests. Time will tell.
I too practice saying the triple and double tonguing syllables, usually when driving. And at work. And in the supermarket.
I did hear that a certain American euphonium player was the unknowing founder of the ‘beat box’ phenomenon, anyone else heard this story?