Nudist, ill-mannered, keeping press out (6)
I believe the answer is:
distil
'press out' is the definition.
'nudist ill-mannered keeping' is the wordplay.
'keeping' indicates the answer is hidden within the clue.
'DISTIL' is hidden in the letters of 'nudist ill mannered'.
(Other definitions for distil that I've seen before include "Refine, extract" , "It slid (anag.)" , "Treat substance through heating and cooling to extract an essence - whiskey?" , "Make alcoholic liquor through heat and cooling" , "Make, eg, whisky" .)