Way I do it once its in the car:

Have someone sit in the drivers seat.
Place rag under the master, where the hard line is screwed on with the flare nut.
Remove cap, fill reservoir.
Have that person push the clutch in a few times, then stop and hold the clutch down.
You break the nut, fluid will come out.
Repeat a few times, making sure the reservoir is full each time. You want a steady stream of fluid to come out a couple times.

After you do that, bleed the slave again.