I'll admit, the bucket thing is a little far-fetched. But like Putnam said, water should be given the properties of a solvent.
Stormcloudy, since I'd rather have you as a friend than an enemy, I'll offer a new idea. This perhaps will be a more realistic way of dealing with a salty foe.
---S--------
----DS----------
------SD--------------------------
------S-------------------------------- GROUND LEVEL
------S--------------------------------
----DDSDDD----------------------------
------SDDD-----------------------------
------S-----D---------------------------
------S-------D--------------------------
--- S ---D---------------------- 2nd CAVERN
-- S F DDD---------------------
-- S ---------------------------
---SSSSSSSSSS----------------------------
----------------------------------------------
- = layers
S = water
D = Dwarf-occupied space
F = Forgotten Beast of Saline Horror
Here we have a basic diagram of the situation. At the fortress in question, I have dug a shaft from a mountain-top brook to the 2nd cavern, which has a few switchbacks I use to power waterwheels and provide water for hospitals. At this point in my fortress's history, I have begun to notice that the water levels in the 2nd cavern are rising, which may eventually flood the caverns. Enter Salt-Monster. If I were to cut off access from the 2nd cavern to the rest of my fortress, the 2nd cavern would eventually fill up with water. The Salty Foe would be trapped in an ever-filling water chamber, and would undoubtedly dissolve over time. Since the brook provides infinite water, I can sit back and watch the Forgotten Beast dissolve. IF, that is, the game were to be changed to make water react as a solvent to certain minerals.
And another thing: what if water could cause rust? Enormous iron corkscrews in your pump stacks and such would need to be replaced often.