Will my large seroma go away? I'm 9 days post mommy makeover.

Seromas should be closely followed by your surgeon.  If the fluid has been absorbed by the tissues around it, it cannot be drained.  If it is in a pocket, it is possible to drain it.  Wearing compression may help it to heal.  Follow the advice of your surgeon and keep all follow up appointments.

The fluid and general area can feel firm or hard as your body builds a scar capsule around it.  You might speed the recovery process with a tight compression garment or spanx.  This can be frustrating after a big surgery like this and it may get firmer before it gets better.  Massage of the area sometimes helps the squeeze out that fluid and break down scar.  Eventually your body will smooth it out as the scar inside softens over time.  Good luck, Dr. Aitken

Dear imchanellove,seromas do occur often after a tummy tuck. Smaller seroma can resolve by itselves but larger ones require a drainage. Based on your description, 400cc is a big volume and it is hard to expect that it will resolve without a drainage. However, your surgeon has a full insight in your preoperative and postoperative findings and you should follow his recommendationsDaniel Barrett, MD, MHA, MS 
Certified, American Board of Plastic Surgery 
Member, Am. Society of Plastic Surgery