Pay attention to what John was saying-

When bleeding the brakes you can toast your existing Master Cylinder by
pumping too vigorously and pumping all the way to the floor.

O-rings in M/C get scrapped up and bye-bye, buy a new one.

btw- Folks have had great success with making a pressure bleeder with a
gardening sprayer, a PSI gauge, a length of hose, a tire 'stem' with the
core removed, and an old brake res. cap with a small hole drilled in it.

Stem goes in new hole in cap, hose on stem, other end on bleeder, pump
up to about 10 psi or so and crack open at the farthest corner from the
M/C, then the next, then the next until you finish with the closest.

DOT 4 is great stuff, ATE makes theirs in Blue and Red so you can see
when you have flushed all the old stuff out.

hth,
TBerk