Gas Pipe?
I'd suggest running with rg20's idea of using plastic pipe. One variant on using household piping would be to use the yellow gas pipe you see used for gas mains. If you ask nicely, most crews will let you take any scrap.
I picked up some 180mm diameter pipe yesterday, which has a 10mm thick wall (so it'll be plenty strong enough). It's also super-easy to work with. I was able to cut the tube to length with a bandsaw in minutes and drilling/tapping it for vacuum feeds would be easy.
Biting the hand that feeds IT
