The size of the siphon will depend on your system...for a big system that needs to drain lots of water you will need a bigger siphon..
I have a small system using a bell siphon in my 20 gallon GB I am using a 1/2" standpipe and return pipe to my FT...The bell is 1"
It did take some tweeking to get it to flood and drain the way I wanted and the siphon does require monitoring and adjusting in the system...If I had to do again I think I would go with a constant flow and use a standpipe to adjust the hight of water I wanted to maintain in my GB...I think that would be less time consuming
Just my opinion