Anyone know a way to get dwarves to clean of excessive amounts of blood? I don't want my electrum bridges to be covered in layers of Ago Fatmalice's goblin blood.
This is difficult. In theory dwarves with the cleaning labor enabled and some free time will go to a tile of blood and clean it up. If all you have is one or two tiles of blood, that will take care of it. The problem comes when you have a lot of blood, and a dwarf who is cleaning up one tile of blood will on the way step in other tiles of blood and get the blood on him. He will then track the blood around and get blood on yet more tiles. Dwarves who have blood on them will attempt to get soap and go to a water source to clean themselves off. This often leaves a pool of blood next to the water source that other dwarves will then step in and get bloody.
Moving water will sometimes wash blood off dwarves, but in the process the water gets bloody and deposits pools of blood on multiple tiles. In theory moving water is supposed to wash blood off floor and wall tiles, but in my experience this just spreads the blood around.
Flooding an area with magma will completely remove all blood from everything in the area, including dwarves. It will also remove dwarves.
Finally, you can run the cleanmap.exe program in DFhack to remove all blood from the map. This doesn't remove blood from dwarves or other creatures, so if you have a lot of dwarves with blood on them you may have to run it over and over again to control the infestation. I don't know if DFHack has been updated for 31.11 yet.
The problem here is that mass isn't conserved with blood and other contaminates. A pool of blood can contaminate multiple dwarves, and a bloody dwarf can make multiple pools, and neither contamination will ever go away on its own. Or if they do, it's slow enough to not make a difference compared to the rate at which dwarves can spread it around.