Sorry I missed the pieces that the carbs mount to in the parts list. Just as "timsatx" posted, that's the part. Threaded on one end and smooth for tubing attachment on the other. There's no actual need for the threads, it's just the stuff I had around when I built it. I cut four slits in the end so the clamp could squeeze it down to grab the carb body. Maybe there is something that would work better. You only need two, not four, since it only has to be attached to the outer two carbs. It's just a general idea of how to build it. Since I originally posted it some time ago, others have made slightly different versions.
So far no problems with carb cleaner. I sprayed the heck out of the PVC with Berryman's B-12, which is mostly acetone and toluene, and it didn't seem to affect it.