In the professor's area, before you get on the hang glider, you'll see a giant horn on a platform.
You'll have to use the little brother to operate the rotating lever and the big brother to use the level that can be pushed. Start to rotate with the little brother. Now move the horn to the right to the 5th pipe. (Unless my eyes are off, it's different from the attached video.)
I found a YouTube video that should help. I didn't make it.