We want to replace the steel piping used on Spencer central vacuums. These are in rental car facilities and have 8 drops on them. The problem is that because they are steel, the inside quickly rusts from sucking all of the sand. The rust traps the other stuff sucked up and then we have to go out and auger the lines. So I was thinking of using pvc lines that wont rust and start the process. The problem I'm having is matching the OD of the steel pipes with the OD for the pvc. Trying to find an OD of 5", 4", and 3", or something real close to it. Any thoughts on this?