I have searched and can't find the differences between Duck and Goose fat for soaping. From what I have read they are quite similar. So going forward, many years ago I was in Prague and sweet-talked our waitress into bringing me a BIG box of goose fat to take home so I could render it to bring back to the States.
I was at my son's house and we pulled out all the pans we could find, tossed in the hunks of fat and the oven was stuffed full. Ran to Ikea the next day and bought a bunch of airtight metal lard tins and when the lard was cool enough poured it in and dispensed them between my husbands and my suitcases and held our breath that we wouldn't get caught--was just going to play stupid, if I was told it was a no-no. It wouldn't have been much at that time as our dollar was very strong compared to the Czech crown. Made it home safe & sound. I made the nicest soap out of that lard, I just found one of the recipes that I made using it, called Goat's Milk Cinnamon Oatmeal Bar. The oils & butters I used were Castor, Olive, Safflower, Soybean Palm Kernel, Jojoba, Goose Tallow, Oatmeal & Cinnamon.