Island sink with typical dishwasher, garbage disposal hookup not draining properly. Any draining is slow beyond practicality and backing into the disposal. Yes, an AAV is connected downstream from p-trap on riser just under the counter. Ran a snake down the wye and 25' into 3" connected to main sewer line drop. Nothing of consequence was pulled out...Connected trap and wye back up and tried again with no good results. Thinking plugged further down the 3" line I hooked up a balloon hose rig to an outside hose bib and ran 5 min. worth of full valve water into the drain. That worked well with no backup. So...hooked up system and tested...still not draining. Suspected the AAV after the water test. It is not accessible to unscrew without removing the sink, etc. or cutting the 2" riser pvc. So before I cut pipe I did another test and drilled a small hole in the riser just below the AAV. As I completed the hole a pressurized jet of drain gas blew out with a rush. With the hole left open a modest volume of water would now drain but increased volume would start to rise in the sink tailpiece and disposal. An large amount of dumped water would back up and exit the hole with force, which by necessity, was a bit below the sink water level. Finally the question, could the problem not be a faulty AAV but possibly a compromised main vent system many feet away? Maybe a water hose down the roof vent pipe is in order before I replace the AAV?

Thanks for input.