This was a problem I had with my 2014. Santa Fe has lots of dirt streets so if the weather has been dry for a week or so, dust kicks up behind the car and lots of it would seep into both the lower and upper hatch interior seams. It was a constant and annoying cleaning job. The first time I washed my 2017 I was pleasantly surprised that they've worked to seal almost all of the dust from getting into this area.Then, after every drive (this is what I do) raise the hatch and blow the dust out of the inside corners.
As for managing the dirt, etc. that accumulates on the back end of the car, I start with my power washer and spray the back until there's no more dust / dirt coming out of the various crevasses created by a diabolical engineering / design team.