We live in a condo. Our unit is above the garages of all of the other units in the building. Our AC condensation drain line (I'm not sure if that is what it is called) backed up and caused a flood that went into the neighbor's garage. The plumber came and blasted some air down the line, which took care of the backup on our end, but made a mess in the neighbor's bathroom.

Obviously we are sharing a drain or vent with the neighbors someplace along the line. To me if the air came out in the neighbor's bathroom, there is probably still some sort of blockage someplace. We had the same problem two years ago.

The HOA is dragging their feet on having things checked out and I just wanted to make sure that I am thinking logically before I start nagging them about it.

Nag formally by sending them a certified letter outlining the issue with this COMMON property. You do not own the pipes inside the wall, the association does and they must insure they are working.