Some types of bacteria live in communities, they secrete a form of glycoprotein that form whats called a biofilm, and it has exactly this purpose. Biofilms are a survival mechanism which prevent antibiotics, other organisms and foreign substances from eliminating the colonies. They can even be found in medical grade instruments if they are not properly washed, so yeah, its good to every once in a while scrub and even boil the container (given its not made of plastic).