What Giuliani used to do is not solid (5)
I believe the answer is:
runny
'is not solid' is the definition.
I don't understand how the remainder of the clue works.
(Other definitions for runny that I've seen before include "Inclined to be rather liquid" , "Molten" , "Tending to flow" , "Not set, inclined to spread" , "(Exuding) liquid" .)