Sound insulation of a downpipe passing through the living kitchen

The wall is currently plastered. Would the Armaflex then decouple the pipe from the plaster? And would the angles of the bends (as far as I know, 2x 45 degrees) possibly need to be softened?

You only know exactly how to do it once the wall is open and you see the condition. Normally, the pipe should not touch the plaster and/or the wall already now - without the pipe clamps. So it does not need to be decoupled. And you also need the space to roughly wrap a 20mm thick mat around the pipe. By the way, Armaflex cannot be plastered. Then ribbed steel mesh or similar must be installed.

You can design it in such a way that you don’t hear it. We have the downpipe in the exterior wall in our dining room. It couldn’t be done any other way for us. With insulation using mineral wool, you don’t hear anything here. Neither when showering nor the toilet flush.