Grey Tank Burp

[Steven@147]

Well I was tanking a shower and heard some gurgling noise, then whoosh. Seems air/water shot up through the left (dual sinks) bathroom sink, splashed on the counter and on the bathroom mirror. Well crud, we got the dreaded tank burp on grey tank 1. been ok for a little over two years now we got it as others have experienced. Yup searched and read up on what others have found.
It takes a little while after dumping the tanks but its been doing it the last few times when the grey 1 gets a little in it.
Got after it today checking the usual things. Cleared out the storage compartment , took down the wall, (gosh I just hate looking in there) and sketched how the drain and vent lines are run as best I can tell, some things you just can't see, but made my crude sketch. I'll clean it up later but for now gives me some reference. got up on the roof and took the little black vent caps off. One had some spider webs in it and the roof TPO "U" flap they cut out was partially covering the vent. No indication the vents slid down into the tank any more than what it was.

Going to have to take apart the skeleton frame the back wall screws to in order to reach the shower trap to see if its partially plugged. I'm going to try and pull the shower drain screen and see if I can fish goop out instead of taking the trap apart, I can't reach it. Took lots of pictures for reference. The weird thing is the whoosh comes from the far most bathroom sink in the line, (dual sinks) you would think if it was going to do something like that it would be the sink closer to the AAV, which are fine by the way. I replaced them long ago with better valves.

Well just one more thing too look after. Hey until I got to it today I just stuck the sink plug in tight, be my luck the plug will become a missile next time or if the tank burps again.