I made the venturi on this one:

The copper nipple between the yellow handled valve and the blue handled one has an extension made from 1 1/4" copper pipe, brazed to the end and extending about half ways into the male Banjo coupler. It had nearly as much section as the store bought one I replaced it with here:

The venturi is the tapered top piping. I quit using my old cone because the handler has blades inside for opening plastic jugs and the plumbing alongside the cone is for rinsing the jugs as you empty them. I think the cone, blades, stand, venturi, valves, and plumbing was somewhere around $600.