Since it seems you've caught your duck early with the infection, you can try one pill per day of Bayrtil, 50-100 mg of clindamycin, doxycycline, lincomycen, or 250 mg of amoxicillin to try and cure the problem.
If antibiotics alone to do not cure the problem, you or your vet will need to lance and remove all the infected pus in the center of the growth. Wash and disinfect the foot with a diluted iodine solution. Make an incision with a sharp scalpel and press out all the pus. Then you must flush out all the remaining pus with your diluted iodine solution. Put a pad over the incision, and then try to keep pressure off the incision with a “cast” or a cut up tennis ball over the foot. Keep the bird out of swimming water until it is healed. Continue the antibiotics until the wound is completely healed.
