teeny, tiny rocks
We found the valve for the toilet; it was in the back under the bath sink (behind the drain plumbing). The toilet water is running fine, but thanks Larry71 for the suggestion.
The problem we were (are?) having is when we're hooked up to city water. We tried filling the fresh water tank and turned on the pump and started getting much better pressure, but still very little water, spraying now instead of trickling slowly. So Doug took the filter off the bath faucet and found the problem with it -- teeny, tiny little rocks plugging it up. After he cleaned it out we got full water. The shower head is gonzo, too old and mucked up for a cleaning so we're replacing it. We quit for the day because we started losing the sun, but we'll try it again tomorrow with city water and see if it's better. We think it should be.
Doug & Jamie, AIR #650