Here's how I constructed this in detail. For now, I left out the center rod and air fitting concentrating on the assembly of the center tube (blue arrow) and exhaust pipe (red arrow). I've screwed on the plumbing cap that has the hole drilled for the air fitting (green arrow). Once this is inserted I can line it all up thanks to the white PVC pipe which should center everything nicely in the exhaust tube. If you look at the plumbing cap (green arrow) you'll notice I've ground it down some to make more room for the exhaust to pass. I wanted this to be protruding some so the exhaust flow passes then accelerates causing a vacuuming effect. But the plumbing cap was very rough and lacked the aerodynamics I wanted, so I worked it over with a hand grinder then spent some time with it on a bench grinder to get it smooth and tapered, no rough edges.

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