I've always gravity bled brakes on my cars, but that wouldn't work on my 2013 Acura SUV with ABS. So I used a hand operated vacuum bleeder to pull out all the old fluid. The result was all new fluid in the system and a pedal with erectile dysfunction, very soft.

Bought 20 ft of clear vinyl tube and ran the hose from each wheel cylinder one by one up to the master while gently pumping the pedal a few hundred times. From the driver seat I could see bubbles traveling up the tube. Problem solved. Took about an hour. This same procedure is said to bleed the master without needing to do bench bleeding.

Each wheel cylinder had one discreet batch of bubbles. Once they were gone, the system was good. The vacuum bleeder obviously had sucked air down the bleeder valve threads. Maybe I should have put grease on the threads? Next time I'll try that.