Found the access panel and am able to look up in there and i do see the vent going up the wall to roof, so I guess its vented. Not sure what I can do from here. I dont know if maybe I can install a vent in the line under the sink like the 2 sinks have? Its really frustrating as the tank is right there and I cant see why it backs up. Tried again blowing it all out with pressure to no avail.
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