Typically, we'd schedule a stop at Glory Farm on our way across state, but this year they were crazy busy with 2nd Son's university graduation celebration so we hung a left at Ritzville, headed eventually for Chinook pass.
Hatton Coulee Rest Area featured not only dump stations for humans but also for RVs. Nothing beats a clean, well designed, FREE dump station. On the other hand, maybe that goes in the TMI category.
Indian Creek - a national forest campground on Rimrock Lake. Nice campground that was nearly empty, but didn't have any usable connectivity or solar potential.