A neighbor three houses down called another plumber that did snake the line and he cleared a blockage as it tied into the city line but said that there is another obstruction going the other direction that they are putting a camera on tomorrow.  

Collapses and blockages in sewer lines lead to overflows into nearby streams and basement backups.

And yes you should have your chimney professionally swept/cleaned to ensure there is no blockage or other surprises in there.

Someone was clearly negligent here, however, I cannot prove responsibility and the blockage was found in unit 1.How would you go about charging the plumber bill?

Cash blockage?

stick your hose or whatever in there and see how far it goes, then lay it on the ground above the pipe and you will see were the blockage is.dig it up, cut the pipe in half, and get the junk out of there. if it is black corragated 4 inch pipe, then you can get a coupling for 3 dollars at home depot and then wrap some duct tape around it. if its DWV pipe or SDR just go get a 4'' coupling for 3 bucks and slap that baby on there, glue is preferred but not needed, there is no pressure.if you are having trouble locating the blockage, try runnin the hose from the drain end of the line not from the gutter downspout end.hope it works, steven

For example, if the main drain has a blockage and filled with water, and someone unknowingly flushes the toilet, the positive pressure created by the flushing action had no where to go due to the blockage, in a conventional atmospheric vent the positive pressure can just be relieved, but not with an AAV.In some jurisdictions, they allow you to upsize the drain line in order to allow part of the drain to serve as a vent.Also, try to explore an option where a conventional vent can be implemented in the island, but creatively disguised as a support beam, a decorative pole or something.

Blockage could be caused by a multitude of things already named, as well as silly things like balls or dead birds, or even a collapse of the pipe upon itself somewhere underground.

Kind of unusual but we will never have an issue with tree root blockages.

They are concerned there may be blockages in the "Main Line".