Pipe diameter associated with showers (5)
I believe the answer is:
drain
'pipe' is the definition.
(I know that drain is a type of pipe)
'diameter associated with showers' is the wordplay.
'diameter' becomes 'd' (mathematics).
'associated with' is a charade indicator (letters next to each other).
'showers' becomes 'rain' (rain showers).
'd'+'rain'='DRAIN'
(Other definitions for drain that I've seen before include "Draw off liquid" , "Exhaust (of liquid)" , "Bleed" , "Deprive gradually of strength or resources" , "Waste channel/pipe" .)