I'm not sure of a diagram but I think if you follow the tube that comes out of the passenger exhaust manifold and goes forward, you'll find it at the end of the tube. People have had them plug up (I've never checked mine in 200,000 miles...) and they have had success screwing a grease gun onto the tube and forcing the grease and gunk all into the exhaust then blowing it out with some compressed air.
Borrowed this from one of our more intellegent members. Sorry I can't give credit to the proper person. I saved it for future use and do thank that member that took time to do this and post it. Maybe it will help.