Epson salt soak, clear iodine, and triple antibiotic cream without pain relief. You want to start with a soak in the salts for at least 15 minutes. Then apply the iodine, let dry. The apply the antibiotic cream and wrap the feet. Keep the duck on clean dry bedding until you can get the bumble out and healed.
I know you have to remove it but I don’t know enough to talk you through that part.
Don't let the duck drink the Epsom salt water. Gives them diarrhea! @casportpony@Miss Lydia can help with treatment too. Start with what @Knighstar679 said!
Wear gloves when working with bumblefoot, it's a staphylococcus infection. Nutshell version, soak feet for 20+ minutes in WARM water, epsom salts help a lot, but not mandatory. Try to "pop" the outer scab off. Once that's removed, gently squeeze the infection out. The pasty, gummy stuff is bird-pus, it's not all runny like human pus is. Expect the quantity of pus to be profound. If all is not removed, the infection will simply return, so patience while you work. https://the-chicken-chick.com/bumblefoot-causes-treatment-warning/
I just finished getting the kernel out of one of my hens foot. I had to do it 2x before I got it all. Soak and use clear iodine over the entire bumble then put on the antibiotic ointment or not you don’t have to wrap until you get the scabs off and get the kernel out then you wrap. To keep it clean while healing keep soaking and using the iodine until the scabs peel off easily. Don’t be in a big hurry so you don’t tear good skin.