We had one when we replaced the plumbing and put in a septic tank (when we first moved to the HomePlace). Living outside the city limits, there were no regulations against one. Sanitation during an emergency is vital for your health and the health of those you protect and provide for.
Ours was located down a path through the woods at the edge of the back pasture, far enough away from the house to avoid nuisances like bugs and smells. It had a transparent moon roof at first. You could look up at the remarkable skyfull of stars at night, but during a hot summer day it suffered from the greenhouse effect and became an odd smelling sauna. The moon roof was covered shortly after that. Want to see the stars? Open the door! Small windows for light were added at the top sides instead.
TP was stored in a water-proof plastic box with top until needed. Rain occasionally found its way in through the ventilation.
We kept a covered coffee can of ashes from our fires next to the TP. After each visit a person sprinkled ashes over their deposit to keep the smell in reasonable limits, discourages some bugs, and help the "product" break down fast. Save those ashes!
It had a lovely toilet seat installed to avoid fanny slivers, and add to the homey atmosphere. We posted a few pictures to improve the decor, provided some reading material, and it was perfectly adequate.
Built on skids, when the hole below reached capacity, Art hooked the Outa-Backa up to the tractor and pulled it over to the new hole. Shovel a thick layer of dirt over the previous hole, mark it carefully, and begin again in the new location.