Installed two 4" DWV siphons that ran fine for one week until they simultaneously(within a couple of hours)stopped. The head difference between the pond water level and the siphon outlet is 3 feet. The lift to get over the dam is now 5 feet instead of the original 2. The siphon inlets are not clogged. The lift section is a little "out of round" but definitely not crushed from pressure. I extended the siphon outlet, gaining another 4 vertical feet, but cannot get siphons started.

Whatcha think?