Whatever container you buy or make, its best hung or situated wel above the cage if possible so gravity assists flow. I your cage is quite strong the smaller ones can be sat ontop, though any considerable weight will ofcourse warp/stretch the mesh, so its not the best idea.
Alternately and perhaps a better solution, is to use aquarium tubing from the container
down into the cage, and preferably, somewhere between (for convenience) an aquarium tap type valve so you can adjust, turn on/off flow.