I just received my package and used one of my sheepskin mitts on a really dirty car. After I was done using it, I tried to thoroughly rinse it and hang dry. It was obvious there were some black marks in the sheepskin that wont rinse out, seems to have stained it black or just wont wash out. Im afraid there are fine particles of dirt and grime in the mitt thats going to end up swirling the car all over. How should I properly clean it?