siphon-tap

from The Century Dictionary.

• noun A contrivance for tapping metal out of a furnace. The molten metal rises through an oblique channel to the bottom of a reservoir outside of the furnace, in which it rises to a higher level than it occupies in the furnace on account of the blast pressure and the weight of material in the furnace, and from which it can be ladled without disturbing the furnace. It is used commonly in lead-furnaces under the name of Arendt's siphon-tap.