If you just want to work with the piped output, use it like this:
docker run --rm --log-driver=none -a stdout -a stderr alpine seq 1 20 | hexdump -C
(Hint: adding -t for an interactive terminal will break the output.)
If you want to pipe something into the container and work with the piped output:
seq 1 20 | docker run -i --rm --log-driver=none -a stdin -a stdout -a stderr alpine hexdump -C | cat -
(The second will not even with the -t option, though it will require -i to process the piped in data)
Both commands result in the same output on my Ubuntu 18.04 / Docker 19.03.5 machine.