I'm setting up ducts on my foundry to filter each of the ores that it's melting and I've come across a couple of the molten buckets that can't be placed in the duct: desh and ostrum. Both of those items show say they're from KubeJS, while all the others that do work are from Hepthaetstus.

Found a workaround: The filled copper cans from Hephaestus/Tinker's work as the duct filters and I've not run into any materials that it won't accept yet - both Desh and Ostrum work with this method. Wish I'd noticed the icon that shows in an empty duct is the copper can and not actually the vanilla bucket sooner!