FWIW, I did a little testing with our Oxygenics showerhead a couple years ago and found that keeping the flow as low as possible but still getting a spray effect, it would consume .6 gallons per minute.
Now, as far as toilets go, I read about people saying "use plenty of water " for the black tank, as well as many saying that they can go 2 weeks before dumping the black tank. How much should you put in the toilet between flushes?? We put about a quart of water in (I've measured it!). Too much? Not enough? With a 41 gallon tank, we can go a week max before the dreaded burp.
JK