this is the only correct way, could still be improved with more trough along the back wall

If it is particularly taters out it can be done by clenching your teeth, lips together but not firmly closed, saying ‘buh’ and blowing. The ‘rrrr’ is produced by your lips flapping together. It is quite fun to do

the comic posted here is an edit of this one: https://pizzacakecomic.com/post/717668298399023104/magic-school-bust