I have never in years of duck keeping had a duck with classical bumble foot (touch wood).
I have on occasions had a duck with a foot lesion like yours
@edtheduck. This sort of injury can, I believe, develop into a full infected bumble with pus inside. I have tried using epsom salts soaks, the treatment for bumble foot. But epsom salt soaks dont draw pus from a dry wound as there is none. My ducks do not like being stood in a bucket of luke warm epsom salt solution. They also don't like the necessity of wrapping their neck in a towel, to stop the duck drinking the epsom salts (which would give the duck diarrhea).
So, I manage these wounds by washing the foot and keeping it clean. I use regular tap water and dish soap if the foot is very dirty, taking care to rinse the foot well. You might spray with vetericin if you like. Then cover the foot with a dry dressing and use waterproof tape to hold the dressing over the wound.
I would keep the duck in a clean dry place such as a temporary pen or large dog crate for a few days to give the wound chance to dry up and heal.