The drawing shows a vent already on the toilet...without the AAV.
Try removing the AAV and see if this helps the flush. It should unscrew from a female adapter. However, I dont believe the issue is venting. It could be the ports in the toilet are clogged with calcium buildup or the flush valve needs to be rebuilt. Just a couple of other things to look into.
Try removing the AAV and see if this helps the flush. It should unscrew from a female adapter. However, I dont believe the issue is venting. It could be the ports in the toilet are clogged with calcium buildup or the flush valve needs to be rebuilt. Just a couple of other things to look into.