Describe the machine the attendants use on Mildred.

From the text:

They had this machine. They had two machines, really. One of them slid down into your stomach like a black cobra down an echoing well looking for all the old water and the old time gathered there. It drank up the green matter that flowed to the top in a slow boil. Did it drink of the darkness? Did it suck out all the poisons accumulated with the years?