One who can't even put a washer on a faulty tap? (4)

I believe the answer is:

drip

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'one who can't even put a washer on a faulty tap?' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'one who can't' is the wordplay.
'one who' becomes 'dr' (from TV series Doctor Who).
'can't' becomes 'ip' (I am not sure about this - if you are sure you should believe this answer much more).
'dr'+'ip'='DRIP'

Can you help me to learn more?

(Other definitions for drip that I've seen before include "Fall in small drops as from tap" , "Dribble" , "Weak and ineffectual person" , "Slow leak" , "Leak slowly" .)

I've seen this clue in The Globe and Mail.

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