Two-story 90s home, double bowl with disposer, AAV in the cabinet, smell shows up 10–15 minutes after a load of laundry; trap stays full. I’m leaning toward a tired AAV plus washer pumping air into a borderline vented branch — any quick way you confirm it on a service call without smoke? I can swap the AAV, but I’d like to verify before I start cutting.
Try a quick “peppermint test”: drip a teaspoon into the washer standpipe, run a drain, and see if you smell it at the AAV/disposer — your nose is the smoke machine. @OP if it shows up fast, swap the AAV and confirm it sits 4"+ above the trap arm; if not, check the dishwasher high loop and the disposer splash guard as alternate leak paths.
@OP quick check: pop the AAV off, slip clear tubing on the adapter and drop the other end in a glass of water, then run the washer — if it bubbles or the water column rises, you’ve got branch positive pressure and the AAV/venting is marginal. If it stays calm, look at the non-vent culprits like a gunky disposer splash guard or dishwasher tie-in burping odor when the pump hits, like a cheap lie detector telling the truth. Do you have an air gap or just a high loop on the dishwasher drain?
@paul_eva11’s pressure-check is good; as a cross-check, tape plastic tight over the wall stub-out/escutcheon and the cleanout in the cabinet, then run a laundry drain — if the plastic balloons, the branch is going positive and you’re smelling it from the wall, not the AAV, . If it stays flat but the odor shows, swap in a new AAV rated for higher DF and retest. Is that kitchen tie-in upstream of the washer by any chance?