ˈ ̷ ̷ˌ ̷ ̷ ̷ ̷ noun
Etymology: down (II) + comer
: a pipe to conduct something downward: as
a. : a pipe for leading the hot gases from the top of a blast furnace downward to the dust collectors and flue system — see blast furnace illustration
b. : a tube larger in diameter than the water tubes in some watertube boilers to conduct water from each top drum to a bottom drum under the influence of thermal circulation