Drain care

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My mother is currently in the hospital and she recently underwent a mastectomy. I'm American Born which makes communication with the doctor's difficult (my grasp of the local language allows me to buy groceries and that is about it as I'm anti social and don't go out much). She will come home with a drain. It is the kind with springs in it, a tab to let the stuff out, and a clamp on the line. They say the line has to be drained, the pack empty, and reset? How do I do that?