The nipple is straight, so I could see into it easily, the other end has a 45 degree bend pipe on it and I couldn't see into that end easily, that was what I was trying to remove. In the end I could not remove it, but I could see through it with a flashlight inside, and I could see we removed the blockage. I can see easily into the new part, and clearly the ID is much larger than the old part that still has build up inside.

I need to figure out what was used to seal the parts together... no doubt this prevents hot gases from escaping. I was thinking of using plumber's putty.