I’m guessing the ABS module will have trapped some old fluid even after a full flush of all the other lines.
Does this mean there needs to be two flushes done?
The initial flush of all four lines going to the calipers then a modulation session of the ABS pump with a scanner to release the old fluid within, then another flush of the four lines.
Or is there a method that is easier?
What year?
Tester
99 pontiac grand prix se 3.1
As long as the hydraulic brake system wasn’t opened, you bleed the system the conventional way.
That would also remove old brake fluid from the ABS.
Tester
That writeup has not one mention of ABS module in any way shape or form.
I’ve done plenty of conventional brake bleeds but never a full flush of the complete system.
My only concern is trapped fluid in the ABS module.
After more searching I found an article that stated:
“On their own, gravity, manual or power bleeding methods can’t completely flush the volume of fluid that is in the ABS modulator. Inside the modulator, there might be as much as five ounces of dirty fluid after flushing. The only sure way to flush this fluid is to use a scan tool to actuate the valves in the hydraulic control unit. Be aware that the worst fluid is trapped in the ABS valves and passages due to their non-integral design.”
I guess I’ll stick with the scan tool method 
Tester
No ABS experience myself, neither of my cars has it, but I expect the gravity method would still work on the ABS unit; I can’t imagine any reason it wouldn’t. But there indeed could be solenoid-actuated valves inside the unit that have to opened electronically using a scan tool presumably for any bleeding method to work.
Note , seems like there may be a diy’er work-around method to open/close the abs solenoid valves not requiring a scan tool. Googling might find it. Another idea, a parts store might rent you the necessary scan tool.