Backwash, rinse, filter blows junk back in pool, possible waste line issue

[PoolDoc]

I think I have determined that my waste line is plugged?

Sounds like it is.

If you need a temporary solution, you can probably buy locally a backwash hose, clamp, and threaded adapter that you can use to replace the hard line. They're available on Amazon, but only with poor ratings, so I didn't link them.