You can fill them, but not pour back? Could you explain on that.
You have to take the inner bag out of the cardboard box, tip them up, yank the spout out, and pour the liquid in without spilling anything, and then squeeze the air back out. It's not terribly difficult but it's too inconvenient to do this every time you develop. It's better to use a bottle or something. It's fine for chemicals that you just fill it up and then use all up.