Yes that is what I meant. It wasn't clear.
I'm 63 and have been digging up sewers that long. They may start at the bottom but they will curl around and come in, not at the bottom, where there is a steady flow. After I learned that I watched for infiltration points while digging up sewers. It seemed true. I think if you pay attention to the next root removal and using the camera you will see entry points are not at the bottom of the pipe.
That closet flange pic is a good debunker but, dare I say,, its a little different.
I think we may have different type trees here than you to possibly. If you still live in Idaho, I’m positive of it. 🤣✌
We have trees that grow in water, they’re not scared of water, especially nutrient rich water. Look up “ Bald Cyprus “ trees and live oak trees.
They’ll grow into the pipe at any opening.
They’ll grown between concrete and the pipe and then surround a toilet flange and grow into the pipe. They grow anywhere there’s an opening. I found two like that in just the past couple months. It’s pretty common here.
Our sewers are installed where the most roots are for the trees In our area, 1’- 5’ deep at most.
Look at some of the pics I’ve posted.