Where, in W. Washington, to get a new coat for mum (6)

'where in w washington to get a new' is the definition.
The answer is a location as well as being a singular noun. This is suggested by the definition.

'coat for mum' is the wordplay.
I cannot really see how this works, but
an anagram of 'coat' is 'taco' which is within the answer.
'mum' could be 'ma' (ma can mean mother) and 'ma' is found in the answer.
This accounts for all the letters.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?