I was just like you aqheart when I was starting this. All I can say is I tried so hard to understand the dynamics and such, but in the end when nobody could give me a definite answer I just went out and made my own. It worked but you should test with a fake power outage to make sure the siphon is held.
The only thing I ever had to do was initially suck on the tube so the water would flow, after that I havent had to do anything. Other than that I would say look into what glue you are using. I used some glue that was supposedly safe that killed my fish, after that I just didn't use any glue and jammed the pipes tight and havent had any problems.