I have replaced the front and back brakes and bled the lines. Each time the master cylinder (the one on the left; see below) had to be replenished, however the cylinder on the right (see below) had it's level remain the same.
What is the cylinder on the right? Is it plugged? Should it go down in level when bleeding the brakes?

If you follow the line from the tank on the left it should end up at the clutch slave cyliender on the right side of the transmission.