I am constructing a 3 acre pond where 50% of the area will be 20 to 25 foot deep and the remainder 8 to 18 foot deep. My plan for a drain (ability to completely drain the pond if I need to) is a gate valve for a pipe that runs horizontally through the dam just 18" above the pond bottom. What diameter PVC pipe should I use if I want to be able to drain the pond completely within 48 hours?Thank you!