Hello, Unfortunately, draining blood or bloody fluid is not normal except in the first day or two. Dark color indicates blood that has been 'sitting around' under your skin for many days. You should keep in contact with your doctor for frequent follow ups until it has resolved.
40 ml of dark red blood in the drain at 18 days after tummy tuck may be a little hematoma that has liquefied and has finally drained. The volume by itself is not concerning, but if the drainage picks up or continues see your plastic surgeon for an evaluation. Usually at 3 weeks, drains are ready to come out. Kenneth Hughes, MD Los Angeles, CA