Strain of bird, assumed a boiler? (5,3,3,6,2)
I believe the answer is:
polly put the kettle on
'strain' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'bird assumed a boiler?' is the wordplay.
I cannot really see how this works, but
'bird' could be 'poll' (poll is a kind of bird) and 'poll' is present in the answer.
'boiler?' could be 'kettle' (synonyms) and 'kettle' is present in the answer.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for polly put the kettle on that I've seen before include "Request for a bird to boil" , "something to feed to children?" .)