You will use the drain to measure the fluid daily, and keep a record of how much blood and lymph is removed. As the volume of fluid decreases, swelling around your surgery site should decrease. When the fluid volume is 30 ml or less in a 24-hour period, you can have the drains removed.
This illustration shows the location of two surgical drains. The model has a sentinel node biopsy to check for metastasis, so there is a drain line close to her armpit. She has also had a mastectomy with immediate reconstruction, using a tissue expander. A second surgical drain has been placed around the temporary breast implant to collect blood and lymph. These drains help prevent lymphedema and hematomas from developing.
See Surgical Drains With a Simple Mastectomy