Here's a new thing I've tried in a few lessons.
Buzz a note and, as you sustain a nice mezzo-piano buzz, gently cover the end of the mouthpiece with your finger so the air can't escape.
Do it correctly and the note will stop.
Here's the interesting part, pull your finger away and the note should start right away, sounding like a clean attack.
In fact, I've done this repeatedly creating the effect of repeated attacks. While I'm not wild about how the notes end, I've like the way the buzz begins with a nice clean "pop."
Hopefully, that's the role of our friend/enemy, the tongue: release the air all at once so the lips can pop right into vibration.
The great thing about "tonguing" with your fingers is that it reminds you to deliver a nice supply of air/fuel from the lungs without any throat nonsense. It should be simple:
air flows - lips buzz
Come to think of it. Should we really be calling this "tonguing?" It seems that maybe the tongue had a really good publicist and managed to steal the spotlight.
(yeah, I considered superimposing some image of a tongue onto this picture but then thought better of it)