Oh, goody! I may have to try that one! How long does a mosquito dunk last before you have to replace it? I've never use one for anything....

Mosquito dunks supposedly last 30 days, but I would think it would depend on how much you refill and empty the watering can.
But they do last 30 days when used in water gardens to control mosquitos. I go through a lot of them in the summer in my ponds.