Is there a way to clean blood from floors inside without dfhack?
I don't know if a lot of people know this, but:
Yes, absolutely, and on command!Any time a building is completed (not when it is removed),
all of the tiles it occupies will be cleaned of all contaminants.Applications:
To clean large swathes of ground at once,
paved roads work well. Roads follow the same placement restrictions as farm plots: In a rectangle of any shape up to 10x10, all of the unobstructed ground tiles (for dirt roads, this means dirt ground without trees but shrubs are OK; for paved roads this means dirt or stone floors without trees but shrubs are OK; for farm plots it must be dirt ground without shrubs or trees; boulders obstruct all three just like trees) must be connected and there must be no buildings of any sort (workshops, chairs, levers, unfinished constructed walls). So if the goblins get into your hallway and you paint the floor red with their insides, order a series of paved roads covering the entire hallway, or at least those parts of it that don't contain traps. (Which you can deconstruct and rebuild to clean, I guess.) If the exposed area is entirely dirt, you can use a dirt road, which is built much quicker and any dwarf can do it immediately (no need for an architect).
If the contaminant in question is dangerous (deadly blood or dust) then paved roads / farm plots may not work, since dwarves stand on them when building, and I do not know the rules on where they stand and when. I DO know that when architecting and building a bridge, they will build it from an adjacent tile. So you can order a bridge (or a series of bridges, if the stain is in a curved hallway; sadly, bridges do not have the flexible shapes that roads allow you) built over the stain, and while cleaning it up the builder will not step on the affected area. You SHOULD, however, make sure that the materials for the bridge are all on the same, safe side of the stain, and if necessary use traffic designations to ensure that they take a safe path to the bridge (if you can't cover the entire stain with one bridge), and if necessary do Science to figure out if dwarves prefer to build bridges from a certain side (I do not know the answer).
My favorite building for clean-up purposes is kennels. Kennels are large (5x5), use 1 building material, are much quicker to build than bridges or roads, and do not obstruct movement at all unlike siege workshops or smaller workshops. Even a dangerous stain can be safely handled by careful use of kennels.
For stains where you need 1x1 precision, constructed floors work as well. As soon as the floor is completed, the stain disappears. If you use this to clean up dangerous stains, remember where builders prefer to stand.
After a clean-up building is finished, it can be removed. I can't quite figure out what rules dwarves use when choosing which side to destroy a building from, so if it looks like someone's about to walk onto a dangerous stain, cancel the destruction order. (With dirt roads, this is not a problem, as they do not actually produce anything that needs to be destroyed.) Constructions are much more reliable, as dwarves follow the same rules for removing constructions as for building them.