Cary: Sorry I didn't have a chance to check this out until now. A nephew called last night about fishing this morning and it worked with my schedule so went fishing until noon and was then busy until a little bit ago. That looks like hilly terrain. If you have enough downhill slope, I think a 4" pipe would probably drain that pond pretty low, pretty quickly and would be a lot cheaper / easier than the bigger pipe. With smaller pipe, you could possibly, affordably use a real check valve on the water side and a ball valve on the dam side to make it a one person job instead of a three person one. With smaller pipe, I'd get a T and small valve for the middle of the dam and use a small gas water pump / hose to fill. That way, a person shouldn't have too much money in the siphon / supplies and one person can easily redo in event it fills back up before contractor fixes the existing. Even with smaller pipe, you'd want to keep it from coming apart so I'd connect the pipes with either self drilling screws or stakes / straps like I did. If I used the screws, I'd probably still put a stake / strap on the bottom end.

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