When bench bleeding a master I use a syringe with a rubber snout on it in the brake line ports. Fill the reservoir about half way and draw fluid out the port, then tilt the syringe to keep any air in it and push most of the fluid back. Repeat with the other port. Re-do until no more air comes out. Cap the port not bleeding, keep fluid in the reservoir. I tilt the master so that air inside it will be forced out the reservoir when fluid is pushed into the port.
This is the one I use but there certainly are others out there:
https://www.napaonline.com/en/p/NMB...fZU3S3UlNqXiPyahJC7wF3a8xgsaAsZQEALw_wcBA pressure bleeder or just manual operation of the master can be used too. Keep the ports plugged as best you can while the master is installed to help keep air out. Usually fluid dribbling from the reservoir out the ports will keep air from coming in.
