How can fat necrosis liquify and drain if I do not have any open wounds?

Congratulations on having undergone the breast reduction procedure. Areas of fat necrosis can be treated surgically;  nonsurgical management is an option also. If the area of fat necrosis is small, it may take a few weeks or months to dissipate;  for larger areas, it may take several months (or longer).  Sometimes, patients will experience drainage as the unhealthy tissue liquefies and makes its way out ( This often happens through the "path fo least resistance", which is a suture line).    In some cases, where the fat necrosis remains longer-term, patients need to consider the pros/cons associated with excision.  Overall, if the area can be excised, without causing significant "deformity" or breast asymmetry, I would recommend excision (so as to avoid interference with self breast exam and/or breast imaging).
 Best wishes.

Dear Dawnellie, 
It is very important that you follow up with your surgeon for your post operative instructions and not from patient reviews on the internet. Your surgeon knows your proposer diagnosis, what techniques were used during your procedure, where you are in the recovery phase and thus will advise you of the best treatment plan to ensure your recovery process. 
Best regards, 
Tarek V. Copty, MD FACS

I think you are referring to a haematoma, not an area of fat. By the sounds of your description the hard area is likely to be a collection of blood called a haematoma. This is made up of your body cells, and likewise your body will see this as being in an unnatural position and will gradually absorb it deep to the scarring.  It can take 6-8 weeks to absorb. There is no need for it to come to the surface and drain to the outside!  The same is true for an area of fat necrosis, although rarely this one can harden and calcify, in which case it wont absorb much.