There probably are tubular drain fittings you could use, but you're not likely to find them outside a specialty plumbing outlet if you insist on using
brass (a very old-fashioned and expensive way to go). Slip-joint extensions as short as 4" are available. Tubular drain pieces (such as you are using) do
not mix with copper DWV (drain, waste, & vent) items except via the use of special adapters. Similarly with Schedule 40 plastic and galv. steel DWV
pipes. Dimensions in each of those systems are "nominal".