Visiting a home in Naperville to replace a relay in their older NuTone central vacuum, I came upon this:
Somebody (basement contractor?) had used 1.5" DWV plumbing pipe to extend this central vacuum line. This creates a ridge at the transition which can catch debris -- a major "Bozo no-no" and an invitation for clogs. I corrected that for the homeowner, as well as this little gem:
The power unit in this case is to the right. The tee on the left, while pointed in the correct direction, is what's known as a "drop-out tee" -- that is, dirt traveling horizontally will fall into the branch line, instead of making it all the way back to the unit. The tee on the right doesn't have this problem, but it is pointed in the wrong direction, forcing the dirt to make an almost-U-turn; another invitation for clogs. Fortunately, the fact that whoever did this used foil tape instead of PVC glue made it rather easy to take apart and re-do properly. This system now works better than it ever has.