ABSOLUTELY TRUE!
Not enough enough volume to reach what is called “scouring velocity”.
The solids fall out of solution in the houseline sewer, build up at the dip of the pipe, and eventually plug the whole house system up.
More money in my pocket when I was in the trade!
Solids don’t fall out of solution. They could, however, fall out of suspension.
We just had a similar occurrence. We need to have our sewer line cleaned out at least once every two years.