Following the advice given on p. 121 of Learning GNU Emacs, 2nd Ed.,
I'm entering the command sequence:
C-c C-o, immediately after executing a command in my Emacs shell buffer.
And I'm seeing the output from that command get flushed, as expected.
However, the flushed output is not making it into my kill ring.
When I move into another buffer and give the command:
C-y, I don't get the flushed output.
Instead, I get the last thing I copied in Safari, using:
I'm on a MacBook Pro running MacOS X 10.13.6 (High Sierra). And I'm running Emacs v26.1, from Emacs for MacOS X.