We don't have synonyms for downspouts yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are downspout and downpours.
(n) :
A vertical pipe or conduit that carries rainwater from the scupper, guttering of a building to a lower roof level, drain, ground or storm water runoff system.
(n) :
A vertical pipe or conduit that carries rainwater from the scupper, guttering of a building to a lower roof level, drain, ground or storm water runoff system.