Here is a pretty good explanation of the theory behind how a Bell Siphon actually works. While his sizes are a bit hard to fully discern from his sketches, the theory is spot on and I especially like how he mentions the need to have the air space inside the Bell within a certain range (between 0.5 and 1″) in order to make everything work.

It is little information like that, that you cannot get from reading most literature on the subject. And this is why it is so useful to have a resource where you can see these things in operation and also talk to people that have built them and made them work in a variety of situations.