Hi all...I just bought a used Walker mower and I used it for the first time on a yard today and got covered in the debris and dust...I know it is semi-dry out but I got covered in more than just dust. Is there a screen that I am missing on the back grass handling system??? Or is the back dump door not sealing tight enough? Any tips or suggestions to help me? Please let me know, I would greatly appreciate the tips and suggestions!