44 gallon fresh tank here, and almost exclusively dry camp. Two of us doing the navy shower routine can make that last 4-5 days. We only use the toilet at night, no dish washing really as we're almost 100% paper or plastic plates, utensils and cups, and bottled water for coffee and drinks. If I really want to know how much water is left in the tank, it can be seen via peeking through the access hole under the rear bed. And if it's low, that's why I carry around a 5 gallon sized one of these:

In reality, my limitation is the 29 gallon grey tank. 8 or 9 showers and it starts to back up the drain.