Traveling the 3500 miles in June, we never once thought to check the  Garmin to see if it could locate rest stops.  We were always looking.   The Interstate Highways provided full service stops at regular intervals  until we got into Arizona.   According to the locals, the state is out of  money. Most of the rest stops are barricaded.   Fortunately the main gate facilities at Grand Canyon National Park (south rim) had restrooms with all the  right stuff:  running water, sinks, and toilet bowls.  And, on the backs of the  stall doors you could read the details of how the water got there (from the  north rim) and an intricate drawing to explain how it is recycled back to  your next flush.  (A few of the particulars confused me, but ..oh~ never  mind.)   Farther into the park, where no water is available, there are outdoor  chemical latrines with huge black vent pipes.  I don’t know the physics  involved, but I can tell you this:  when...