I guess my photo didn't post so I'll try again. I'm pretty sure this is some kind of pipe lining since it's in ALL of the original pipe in the house. In most places, it's still nicely coating the entire inside surface of the pipe. In some places it's broken free and is flaking in big chunks and in this one place it was completely packed. I've already repiped one of the two bathrooms during a remodel and I'll be remodeling the other bathroom very soon and will repipe that one then. Then I'll just have to run new lines to the kitchen and replace a few other short runs. I just hope what I have now will last for another year since I'm about to undergo shoulder surgery and will be recovering from that for 6-12 months before I'll have full use of my arm back.