I've been experimenting with the bell syphon recently and came across the following situation. The syphon worked great during my experiments when test filling the bed with the garden hose, but when I switched over to my pump the syphon did not engage. I went back and used the hose method again and it worked. The hose brought water in to the grow bed at a higher rate which led me to the conclusion that the flow rate of the incoming water has to be significant enough to force the water high enough over the stand pipe to create the vacuum otherwise the water just trickles over the stand pipe and never actually drains. So the question is, is there a "magic" formula for determining the incoming flow rate and/or does the size of the stand pipe relative to the bell syphon also influence the vacuum's ability to engage or not? I'm also curious as to whether the amount of head room between the top of the bell and the top of the stand pipe would make any difference.