Here's The Double Tongue Drill video:
https://youtu.be/uN5SdPviTgk
Not everybody needs a functional double tongue. But if you need it, you need it. After working on double tonguing for decades, I think I have it by the throat. And if a 61-year-old can do it, you whippersnappers can, too.
If you're interested in music at Duquesne University or Carnegie Mellon University, go to https://www.duq.edu/academics/colleges-and-schools/music/index.php or https://www.cmu.edu/cfa/music/ and search my name for contact info.