Dog to get us back in, spotless (6)
I believe the answer is:
pursue
'dog' is the definition.
(I've seen this before)
'us back in spotless' is the wordplay.
'back' says the letters should be written backwards.
'in' indicates putting letters inside.
'spotless' becomes 'pure'.
'us' backwards is 'su'.
'su' going into 'pure' is 'PURSUE'.
'to get' acts as a link.
(Other definitions for pursue that I've seen before include "Dog" , "Follow, chase" , "Give chase" , "Seek" , "Chase, run after" .)