Rainman,
I agree with everything you say except the part about the reason for the outlet elbow. Once the siphon is running, you can cut off the elbow and do almost anything you want with the outlet pipe and the siphon won't stop as long as the elevation change is maintained and the velocity remains high.
The outlet elbow is there to keep the lower end sealed so there's only one place air can get into the system, the vent pipe.
My siphon design is shown in the lower graphic below. The 45 degree elbow connects to the down slope pipe and the trapped water is a very small pool. When the velocity of the water coming down the slope picks up, the trapped pool is cleared out and the seal is broken. The upper graphic shows a typical outlet with a horizontal sealing section. There's no way this seal will get "blown out" as easily as happens in my situation.
I need to fix my outlet. I can either cut out what I have and go with a new horizontal section or I can just add more pipe to what I have and create a deeper pool.
Anyone know why I shouldn't just stick on some more pipe to what I have? That's definitely the easiest fix.
-RFL
