In order to replace all of the brake fluid in an ABS system I always use a pneumatic fluid excavation tool.
Here is an image.
Honestly, I use this regardless of ABS or not. It will create a vacuum at the caliper and the fluid will enter a waste container. If you use clear tubes you can see if it's pulling air out of the system as well. You continue to vacuum the system with the hand pump until you see fresh clear brake fluid which let's you know you have all of the old fluid out.
It's very effective and if you continue to replace the fluid as you pull it through air will not enter the brake system.
Here is the procedure for removing all of the brake fluid from your system and ensuring that the front and rear control circuits are properly bled.