Later they escape with the trash. Maybe that's another movie....but presumably the Death Star ejects its trash too. Why do they need a trash compactor if they are going to shoot it all into space? And how does some sort of creature live in there? Doesn't it get smashed and/or ejected? And why is all the trash metal and fluid?
It's a good metaphor for the whole series - I enjoyed it much more when I was 10.