If you’re also doing a master cylinder replacement, blow compressed air through the lines to flush all the old, contaminated fluid out. Do it before you mount your new wheel cylinders. Bench-bleed the new master to get any air bubbles out of its internal passages. In the old days you’d bend up a couple short lines so the fluid would go back into the master, but most replacement master cylinders now come with plastic caps for bench-bleeding. No fluid can come out of the ports, but the bubbles are free to purge when the piston is stroked.