Why one visits bathroom without posh rug (6)
I believe the answer is:
toupee
'rug' is the definition.
(I've seen this before)
'why one visits bathroom without posh' is the wordplay.
'why one visits bathroom' becomes 'topee' (I can't justify this - if you can you should believe this answer much more).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'topee' enclosing 'u' is 'TOUPEE'.
Can you help me to learn more?
(Other definitions for toupee that I've seen before include "An American wig or hair-piece" , "Artificial hair" , "A wig for American male" , "rug" , "An American man's wig" .)