If I read this right, there is a 5 foot difference in the heads at either end. I don't know the viscosity of maple sap, but it may be just high enough to slow the flow to some small value (combined with pressure drop from friction of the fluid with the pipe). Have you tried it with plain water? That would answer the question about viscosity, because water would flow, regardless, though it might be slow. Next part- once you put a suction on the line, the flow, once started, will continue due to the siphoning effect of the fluid flowing in the line. More fluid on the source side overcomes the viscous flow and/or pipe friction. What kind of pipe are you using?
If you get to thinking you’re a person of some influence, try ordering somebody else’s dog around.
