Thank you for reminding me of this. It is helping me a lot now that I understand a little bit more about what I am trying to do.
Meanwhile I managed to send the dd stream via netcat to a local volume. For anyone interested:
Target side:
nc -l 19000 | dd bs=4M of=/pathto/volume/Sailfish.img
Source side:
dd bs=4M if=/dev/sda79 | nc 10.42.66.xx 19000
Monitored progress with suggested Android 13 and SailfishOS on xperia 10 III - #95 by wetab73 (thank you). It took ages but it looked to be a success.
Will try the publickey move you suggested for further investigations.