Our Max developed a spot like that that turned out to be a seroma .  Some build up and need to be drained and some open slightly and drain by themselves. It seemed to leak more after he would get up and move around. The surgeon had us clean it with hibiclens (can find it in any pharmacy) mixed with water twice a day to inhibit bacteria growth.  Can you maybe send a picture to your surgeon to see what he thinks?  Max's cleared up by the time he had his staples out.  As Jim & Rene have pointed out do not use peroxide to clean it.  I do remember others saying to gently massage the area to help their bodies absorb the fluid. I do recall hearing this is quite common.  Hope this helps you. 

Linda, Bob & Max

You can boil some water then let it cool and use that to clean it with.  Definitely not peroxide.  You could put some triple antibiotic ointment on it just to help prevent infection.  If it's too big of a spot, you could probably put a steri strip on it, but I would check with your vet first.

Donna