Every single outhouse has one (3,4)
I believe the answer is:
bar none
'every single' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'outhouse has one' is the wordplay.
'outhouse' becomes 'barn' (I've seen this before).
'has' means one lot of letters go next to another.
'barn'+'one'='BAR NONE'
Can you help me to learn more?
(Other definitions for bar none that I've seen before include "With no exceptions" , "Without exception" .)