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.
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.
