Actually did read the whole thread, you are right we are expecting different things from our builds. I am building mine so I can stay in it as long as I like. Currently I have 2 tanks (26g ea) and an rv pump, very simple. I usually go 3-4 days before I run low. My wife and I both get a shower out of it. I have never hooked up to city water or a hose.
As for draining grey water, I have 2 40g holding tanks with another on its way.
When I'm finished building, I'll have over 100g fresh water.
If I was doing day trips, I would consider the pressure tank idea.
Up until a year ago I was using the 15 1/2 gal keg with co2 for my beer
(doc says I can't do that anymore)