On the cylinder by were the line goes into the slave cylinder.If the reservior was allowed to run dry than you will need to perform the bench bleed procedure to get a good pedal.
NOTE: When installing dry clutch master cylinder or tube service parts, use alternate bleed procedure (bench bleeding).
Under normal conditions, disconnecting the clutch coupling will not introduce air into the system. However, if there appears to be air in the system (spongy clutch pedal , or insufficient bearing travel), the system must be bled. The following procedure is used with the hydraulic system installed on the vehicle.
NOTE: The clutch master cylinder reservoir must be kept full at all times to ensure that there will be no additional introduction of air to the system.
The downward angle of the clutch master cylinder makes it difficult for air to escape up into the reservoir. Therefore, if the clutch master cylinder is removed from the vehicle and bled while held in a vertical orientation (a bench bleed), air can escape much more efficiently. Clutch Slave Cylinder