Possibly add a check valve in the vertical pipe and a shutoff valve in the horizontal pipe in Detail A for manual starting. In detail B, you could drill a weep hole in a spare 6" threaded cap in the cleanout Y and exchange it seasonally with a non drilled cap. Consider a lesser angle elbow (maybe a 22.5 or 45 depending on slope) on the horizontal siphon break vent. This would allow you to easily extend it deeper along the slope if a drawdown is desired. It would be less vulnerable than extending the horizontal pipe to reach deeper water and probably look nicer too.
