In a ship, it keeps the interior from getting dirty (5)
I believe the answer is:
liner
'it keeps the interior from getting dirty' is the definition.
The definition suggests a singular noun which matches the answer.
'in a ship' is the wordplay.
I cannot really understand how this works, but
'in' is within the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for liner that I've seen before include "QE2, perhaps" , "Removable inner skin or large passenger ship" , "Big ship" , "eg QE2" , "Cruise ship" .)