Where it's residential as far as outskirts of Washington? (6)
I believe the answer is:
uptown
'where it's residential' is the definition.
(uptown can describe a residential area)
'as far as outskirts of washington?' is the wordplay.
'as far as' becomes 'up to' ('up to' and 'as far as' can both mean 'until').
'outskirts of' says to hollow out the word (remove centre letters).
'washington' with its middle removed is 'wn'.
'upto'+'wn'='UPTOWN'
(Other definitions for uptown that I've seen before include "Residential part of a (US) city" , "In a city's residential area (US)" , "US urban residential area" , "Residential area away from the commercial district" , "Describing the more affluent part (of New York, perhaps)" .)