Inject (4)
'inject' is the definition.
(I know that inject is a more specific form of insert)
This is the entire clue.
(Other definitions for insert that I've seen before include "Add in" , "Introduce, put in" , "Place (something) inside (something else)" , "Enter" , "place in the interior" .)
(Other definitions for pump that I've seen before include "Fire bullets rapidly" , "Machine for driving air or liquid" , "Set foot in it" , "Empty" , "ask a lot of questions" .)