We were lucky enough to dive Manatee during the floods last year. It was a lovely, easy kick dive, and I really liked the cave. I wouldn't guess anybody teaches there, though.
Lynne, there are actually a number of instructors that I know that teach at Manatee. The best time there is just before the flood, when the flow goes way down. But even at it's regular flow, there is lots of instruction going on there.