Hello The Bowler Hatted Turner
I did exactly what you proposed in your first post about ten years ago except that I used the grey piping. Worked a treat and easy to use. However, in the first five years I had two dust explosions in the piping which was suspended from the ceiling and ran the full length of the workshop. Fortunately, the explosions were only powerful enough to blow the blanking plugs out of the ends, and frighten the life out of me.
I then ran a bare copper wire down the inside of the pipe and earthed it to the body of the wall-mounted extractor - that was five years ago and I haven't had an explosion since.
Fine dust and shavings being sucked along a plastic pipe are ideal conditions for static build-up, it works similar to a Van-de-Graff generator and in very dry conditions the resulting discharges can cause an explosion - both of mine happened mid-summer.
So, I would highly recommend just adding a wire down the inside of the pipework when you build it. It doesn't have to be copper, steel fencing wire would be fine, just make sure it runs down all the pipework and is then earthed to the metal body of your extractor, or to a mains earth.
I guess the guys who have never had an explosion using plastic pipe got away with it because home workshops are notoriously damp places.
Fortunately/unfortunately, mine isn't! :-)
Cheers - John