Hi,
Brake cleaner is a 50:50 mix of hydrocarbon solvent (usually heptane) and alcolhol (usually iso-propanol) - the hydrocarbon part does the shifting - the alcohol delays the evaporation time.
It will degrease the tow ball and the pads inside the tow coupling quite nicely.
White spirit is also equally effective, for a fraction of the price, but takes longer to dry.
Neither leave any deposit and are safe on metal and paint finishes.
Robert