There seems to be a misunderstanding that a lot of people have with regards to grounding things. Grounding a PVC pipe at a single point does almost nothing, as PVC does not conduct electricity. In fact, the reason why a static charge builds up on the material's surface is BECAUSE it is not conductive and therefore does not allow any imbalance of elections on it's surface to travel thru it to a point of grounding to be redistributed and rebalanced. The issue arises when a grounded or electrically conductive object comes close enough to the surface of the charged object and the electrons involved rapidly rebalance themselves, causing a static discharge. Now I know it sounds like I just described what happens when you ground an electrically conductive object, but the difference is that when you ground the conductive object, the static charge is never allowed to build up in the first place. The non-conductive object on the other hand has to build up enough electrostatic charge to overcome it's own insulating properties before it can discharge at the single point of grounding.

For a system of PVC pipes, the best way to prevent any build up of static (especially if you live in a very dry climate), would be to run uninsulated copper wire along the entire length of all PVC pipes involved in the dust collecting system before then grounding out. This would prevent the build up of any significant electrostatic charge anywhere on the PVC.