Bit confused, but you want the Magmacrucibles to fill up the drums as well as the dynamos? But also want the drums to supply lava to the dynamos like a backup buffer?How can I make priority on fluiducts? I want to feed magma dynamos with magma crucible + lava drums, but if I do that the lava drum fill the dynamos and then the magma crucible stop working because dynamos are full.. Any idea?
Ehm are you trying to pump lava from the drum into the Fluidducts while also trying to fill them with the same Fluidduct network? Why not just run fluiducts from the Magmacruciles to the drums, and then a separate string of fluiducts from the drums to the dynamos?
Try and post a screenshot of what you are doing, its pretty hard to understand from your post alone.