Couples covering pillowcases after sleep: dirty ones need changing (7)
I believe the answer is:
nappies
'dirty ones need changing' is the definition.
(as in a baby's nappies)
'couples covering pillowcases after sleep' is the wordplay.
I cannot quite understand how this works, but
'sleep' could be 'nap' (a nap is a short sleep) and 'nap' is located in the answer.
The remaining letters 'pies' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for nappies that I've seen before include "Cloths for babies" , "They keep babies dry" , "Baby's pads" , "What Americans call diapers" , "They're diapers in America" .)