How is fluid removed with a needle?

About 2 weeks after my tummy tuck surgery, during a follow-up visit, the doctor noticed that it looked like I had some fluid retention (drainage) in my midsection and decided to drain it. He inserted a “big syringe” just below my belly button and drained (sucked out) about ½ cup of red drainage fluid from my belly area. He told me not to look, and I told him I did not want to but I wanted to see the syringe and how much it contained after he was done. I was surprised to see so much drainage was still inside me. He said that it was not uncommon and that by draining it the way he did saves my body the trouble of absorbing it and aids in the healing process. Note: When he first brought out the big needle (syringe) needless to say I was a little apprehensive, but because my belly area was still numb I didn’t feel a thing.