Just wanted to add a data point. We very rarely camp where water is available so we end up taking it with us almost every trip. We always seemed to run out of water quickly, even though we have about 3 times the capacity that we were used to in our old pop-up trailer.
Last week we took our first trip of the year and I installed simple quarter turn inline valves on each of the 3 fresh water overflow lines of our 2007 Seneca 35GS. Wow, what a difference! I'm convinced that on longer trips we were losing almost half of our fresh water.