Use a hammer and nail to make a small hole in the jar lid, just big enough for the sponge.
Trim the sponge to fit snugly and use tweezers to pull it halfway through the hole (soaking it helps).
Boil 1 part sugar with nine parts water until the sugar dissolves, then let cool.
Decorate the jar with bright tape, stickers or flower patterns.
Tie a loop of twine around the neck, plus two more loops so it hangs upside down.
Fill with the cooled solution, check the sponge doesn't drip, and hang upside down in a sunny spot.
Notes
Safety: use plain white sugar only (no honey, dye or sweeteners) and a non-dyed sponge; change the solution and rinse the sponge every few days, more often in heat, so it doesn't ferment or mold. Hang out of reach of pets.