33gal freshwater, about how long will it last?

Our tanks are about 35g each. Our first week long trip we used up all the fresh water and filled grey in 2 days. We had to move campsites anyway, so a stop to dump station was fine. 5 years later, we can last 8 nights. Just have to learn for yourself. We do utilize campground restrooms and showers as much as possible for those kinds of campsites (electric only at most Michigan State Parks).