A method and apparatus for cleaning treatment composition containers are disclosed which are capable of taking out photographic treatment compositions in the form of powder, granules, tablets or slurry from the containers without adhesion of the components to the inner wall of the container and residue of the coagulated and solidified substances and as well as cleaning the inside portions of the containers. The method and apparatus for cleaning the containers for the photographic treatment compositions have the steps of mounting containers filled with treatment compositions in the form of powder, granules, tablets or slurry and comprising as a resin, only high-density polyethylene (HDPE) having a density of 0.941 to 0.969 g/cm.sup.3 and a melt index of 0.3 g/10 min to 5.0 g/10 min to a cleaning apparatus; opening an opening portion of the container to inject the treatment material into a dissolving tank, and spraying cleaning water into the empty container from a nozzle.