I just read another 2 threads discussing this. The question is since you are constantly topping up the master cylinder's reservoir, when do you know the old fluid is completely out?

Another question is about the calipers: there is always a lot of fluid in the calipers' pistons, the more worn the pads the more fluid. How do you remove that fluid completely? Just because there is fluid coming out of the bleed valve does not mean it is (only) the old fluid... I do not think it is worth dismantling the caliper so as to push the pistons all the way back for this operation (too long winded).

And another question about the brake pump: if there is such a pump in the system, might it not have its own reservoir - how do you drain that?