I wrestled with a similar situation. The difference would be that the tile system that fed our outlet was higher than the level of the pond at normal pool. In this respect, we were lucky, but I'm pretty sure that Theo had a tile feeding his #1 pond and he just left it under the surface without any controls.
Anyway, there is so much junk that can find it's way into a tile that I cannot imagine any device that would actually automatically regulate the flow without getting gummed up.
