I have a single hole sink with the dishwasher drain going into the disposal
The wall plumbing has the P trap coming from the disposal into the wall drain. There is an air vent with a P trap entering the wall drain directly BELOW the disposal p trap in the wall drain.
I'm constantly getting back flow from the lower vent trap. Originally there was a double sink and the dishwasher drain hooked into this vent trap. I'm wondering if this vent trap shouldn't be above the disposal trap since I now only have a single sink and there isn't a vent above the disposal trap. It seems it would have gotten air from the second sink before and now there is no air above. Does this sound logical?
When I get back flow it's when I run the disposal and there is some water running.