I have had a major break through tonight. I will tweak it a little come Sunday and see if lightening can strike twice.

And just in time, I have to put this project down now till Sunday, and then can only work on it briefly Sunday as new job Monday.

I will get pics once I have worked this out.
The problem was not the loop siphon, the N, or the M, the flow, or fall or anything else. It was simply that I was draining through the bung hole, and not through the bottom of the barrel. This prevents there from being enough head pressure to engage and disengage.

No clear pics/tutorials/advice via google on how to make a siphon work from the hole in the half barrel. And running through the bottom is not an option.
So I built a siphon of my own design, and it worked on the very last cycle tonight. Let's pray it's not a one time deal.