We just don't have that much waste water. Just my wife and I. We use mostly paper plates and cups, cook mostly in the grill and microwave, so not many dishes to wash. Mostly use water to wash hands and face, brush teeth, ect. Never filled up the 2 gallon tank yet.
Tell me more about the water thief. Sounds useful. I have a collapsible 5 gallon water carrier that I have filled my camper from at campgrounds without on-site water.
Packs easily and great in a pinch.