What does Halacha bring down about nosebleed during a fast? Can one flush out their nose with water? On fasts in which washing the hands and/or body is prohibited, would one be permitted to wash resultant blood off their hands/arms?
O.C. 554:9 says that one may wash his hands to remove dirt or feces. I would assume that blood on ones hands is considered "dirt" for this purpose. One should wash just the area containing the dirt and wash just enough to remove it.
As for flushing your nose with water, you should ask your rav. My hunch is that you're using the water to treat a medical condition, so it doesn't seem like your violating rechitza.