Originally Posted by
drewguy
You go through immigration, customs, recheck your bag and into the transfer zone.
You could very well go back to the same terminal you just were in, but you have to go to the main terminal to clear immigration.
On the way "out" (back to PEK) you don't need to go through customs. The connection you have is a bit tight, but you should be okay. Probably the same terminal.
Customs/Immigration for United is done in the C/D terminal (Midfield?) - all you have to do is to follow the "transferring passengers (Purple line?)" signs when you get out of the plane. Once you clear immigrations/customs you go through security and then go up one level to enter the main C/D terminal. There are monitors around that area to locate the gate of your departure (IAD-EWR).
Re: the transit time at IAD on your way to IAD, it may be a bit tight!