Day18,
I had to have a construction drain during the pond building process and went with a plastic slide gate valve from sepipe. This allows me to drain down the pond to any level I desire. The slide gate valve has no parts to rust and the slide is made from a cutting board material. I have had no operational problem with it during the 2 1/2 years it has been in service. Mine is conventional piping with the bottom drain on the water side of the pond and a trash rack set at normal water level. I just wanted to give you another option that has been working successfully for me.