St. Mary's, KS is a small town, but there is still a place for you to empty your black and grey water and fill up on non-potable fresh water to continue your road trip! Wastewater treatment plants often offer dump station services, and Saint Mary's plant is no exception.
Along with the dump station in St. Mary's, there are other places throughout Kansas where you can empty your tanks. Look for rest areas, campgrounds, and RV storage facilities - all of those places often offer dump station services as well.