I'm pretty sure there's a bus from Tianjin to Huangyaguan. If I remember correctly you can take a bus from Tianjin to Jixian and then transfer to a smaller bus that will take you to Huangyaguan.
I think Bradt have some more information on how to get there:
http://www.bradt-travelguides.com/de...asp?prodid=150
Unfortunately mine is somewhere in a box getting ready to move to another apartment.