Jimmy, thats a good question, that i should know the answer to, i would say pressure test (positive) but setting up for a such a test would be problematic.
and you were going to get us pictures.
once siphon is going it will suck air and you will likely be able to find this with sound. if the leak is below water and small then no problem. if joint is above water and ground you will hear when siphon working, if it is below ground, well, that depends on how paranoid you are.
hopefully you only have 6 joints above the surface of pond. and all of those should be at highest point where vacuum is the least. it sounds like you have high point vent, we could probly devize method to burp the system, nah.
