It certainly sounds like you have two grey water tanks. What they do and how they are hooked up will depend on the model. In my case, one tank is for the outside galley, and the other is for the bathroom and inside galley. I have seen others that have all the sinks on one tanks, and the shower on another (I wish mone was this way). Looking at your floorplan, I am guessing the galley is hooked up to one, and the bath is hooked to the other.
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