My Buff duck had a bumble on one of her feet several years ago. It was quite large, like your ducks and she couldn't walk on it. I tried all of the methods you did by soaking and strying to peel off layers. I work for an oral surgeon, so I brought home sterile blades and tried to work on it, but couldnt get the nerve to be aggressive enough. I ended up having the doc I work for come up and do it for me. He's an excellent oral surgeon and now an excellent duck surgeon too. The bumble went very deep. We did numb her foot with a local anesthesia, incised open and curetted the inside part of the cyst out. The material is very dry and does not remove easily. We cleaned all out, rinsed out with a betadine solution and sewed the incision closed. She stayed indoors on clean bedding for 2 weeks and a baby sock on, and was also on oral antibiotics. Her foot is beautiful today and we have shown her at shows and its not even noticable.