downpipe

From down +‎ pipe.

downpipe (plural downpipes)

1. The drainpipe that connects a roof-line gutter with the ground.
   • 2020 May 20, Philip Haigh, “Ribblehead: at the heart of the S&C's survival and its revival: Ribblehead Viaduct repairs”, in Rail, page 26:

     NR plans to install new aluminium downpipes to carry the considerable rainwater for which the area is known.

• downspout

• pipe down