I'm not aware that the ABS unit has a bleed valve.
I start by siphoning out all the fluid from the front reservoir. What appears to be a single reservoir is actually two via internal baffling. The rear reservoir is difficult to access as it's fill port is just inboard of the bottom of the fill cap. I usually bleed the rears until the fluid is just below the low mark as viewed from the inside face of the reservoir. Then completely fill the reservoir, and tilt it to the inboard side to get the rear res. to fill when the front res. is full.

Then I flush about a quart of DOT 4 fluid through the system using a helper to pump the brake pedal while I operate the bleed valves.

If you have a manual transmission, don't forget to bleed the clutch. The clutch supply line is near the bottom of the front brake res. The clutch does not have a separate res.

Duke