Answer: In order to treat ants successfully, you need to locate their nest if possible. In this case, it sounds as though the nest may be in or near the container, but you will have to watch closely and see. You could treat the container and area immediately around it with diatomaceous earth (must be dry to be effective so you may need to reapply several times), or you could use the boric acid ant baits (Do not apply boric acid powder to the soil where plants are growing or might be grown later as it is toxic to plants) or treat the nest directly with a liquid form of carbaryl(Sevin.)
Good luck with the ants.
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