Tap shoe? (4)
I believe the answer is:
This clue is a double definition.
'tap' is the first definition.
'shoe?' is the second definition.
(I know that Pump is a pump)
(Other definitions for pump that I've seen before include "Device for moving fluids" , "Machine for moving liquids or gases" , "Machine for driving air or liquid" , "Fluid moving device" , "Question - means of inflation" .)