My recent post had a picture of CI pipe under kitchen sink that had rotted through.

Unfortunately, when I cut out the bad section of pipe I found it is 75% full of sludge even where it is pitched properly. Below are pictures.

1) Should I replace as much of the horizontal run of CI assuming it is full of sludge? Or would it be acceptable to try to snake it clean? It goes about 20' before going vertical to below the slab and another 20' to exit the house.

2) What should I do about the run under the slab? Is it likely to be equally clogged?