Ryan,
My pond builder had told me the collar in a top drain system was to prevent leaks from the pipe loosening from the chuging action when the pond has completely filled to the top of the pipe and it cannot vent. Then it will "chug" and could loosen the pipe, allowing crayfish and water to move along the pipe and eventually cause a leak. We thought maybe this syphon system would prevent the chug. I agree that the collar would be a good addition either way.
If the 45 deg was slowly drained, wouldn't it defeat the purpose of having it as a trap? Unless there is some other reason for it that I am not aware of.

Thanks!