The reason for my question is that the original request implied that the “block of concrete” was completely blocking the pipe, but was loose enough that it was not watertight. In that case, the concrete would have to be bored out and the chain knocker vibrations would only work after it was destroyed. But since it had not adhered to the pipe, there might not be any residue that needed descaling. I am not as incompetent as you seem to think. Nor do I need anyone to hold my hand while I am performing my services, either as a “sewer pro”, or as a licensed plumbing contractor, (LMP, to you).