oh wait hang on I've misremembered that story. It was Farkas not Clevenger. It was when he was playing in the Chicago symphony orchestra (probably why I assumed Clevenger) under Rafael Kubelik.
"You heard me, Don't take the water out of your horns!".
"We smiled, and because there was nothing important on the programme except for a lot of loud playing, we simply kept the water in for an hour....
....as soon as it was over Kubelik rushed back and yelled, 'Are you trying to make fun of me? What are you doing with that funny sound?'
....we're not trying to make fun of you, you told us not to take the water out of our horns and that's what we did...
"What difference does that make?" he snarled.
I was mad as hell; I took the slide out of my horn and dumped a teacup of water on his shoe.
'That's the difference', I told him.
Great story