Two named PIPEs (PIPE_in/PIPE_out) connected with `tail -f` | String sent to PIPE_in doesn't reach PIPE_out

1.Create named PIPEs, pipe_in and pipe_out by running: $ mkfifo pipe_in $ mkfifo pipe_out 2.Connect pipe_in to pipe_out: TERM0: $ tail -f pipe_in > pipe_out 3.Send string hello world! to pipe_in and expect it to arrive at pipe_out: TERM1: $ tail -f pipe_out TERM2: $ echo "hello world!" > pipe_in I can only see the string arriving at pipe_out if I kill command in 2.. It seems to be a buffering issue so I decided to run all commands above with stdbuf -i0 -e0 -o0 but it didn't work.