How do you use the spray bottle on Super Villain Island?

The empty sprayer (from Dr. Hare's dream) is filled with the turpentine from Captain Crawfish's dream. Get the red key above the ship's door and opene the chest on the lower deck. Take the green key from the cabinet to open the second chest at the upper left of the first deck, to find the turpentine.

In the Black Widow's dream, click the turpentine, then equip the sprayer to clean the paintings.