I dont understand why people do others work when theyre on the same rank. This is not your boss dumping work on you, this is your colleague. All you have to do is put it back on their desk (if they dumped it on yours) and leave. Come in slightly early the next day to guard your desk from work piling on it.
They get in trouble for not doing their work, while you have done your share.
Just say NO when they ask or demand.