Rinse off residue of fire in vacant Wichita street (4,4)

'rinse off' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'residue of fire in vacant wichita street' is the wordplay.
'residue of fire' becomes 'ash' (I've seen this before).
'in' indicates putting letters inside.
'vacant' means to remove the middle letters (a vacant or emptied out form of the word).
'street' becomes 'way' (road way).
'wichita' with its middle taken out is 'wa'.
'ash' put into 'wa' is 'washa'.
'washa'+'way'='WASH-AWAY'

Can you help me to learn more?