Naive commercial about large plastic tube (8)
I believe the answer is:
rawlplug
'plastic tube' is the definition.
'naive commercial about large' is the wordplay.
'naive' becomes 'raw'.
'commercial' becomes 'plug'.
'about' says to put letters next to each other.
'large' becomes 'l'.
'plug' put after 'l' is 'lplug'.
'raw'+'lplug'='RAWLPLUG'
(Other definitions for rawlplug that I've seen before include "Means of fixing screw to wall" , "Fixer for screw in wall" , "Means of putting screw in wall" , "Plastic sheath put in hole to hold a screw" , "Small tube" .)