No Kim, you don't need one that large. A 3" pipe has more than twice the capacity of a 2" pipe (that whole Pi X r^2 thing). The tricky part about bell siphons is balancing the input flow rate to the size of the siphon. Too little flow and the siphon won't kick in, it just acts like a regular stand pipe. Too much flow, and it won't break siphon at the end of the cycle.Originally Posted by kkedge