Rough plumbing for Washer.....Do I have to have a sink?

Hi, I am adding some plumbing for a washer machine in my addition. My question has to do with the drainage of the washer. Do I have to have a sink for the water to drain? Do I need a P trap? Can it drain directly into the vent? or should it be a seperate pipe? I guess my question is basically what would be the best way to set it up?? Thanks for your time, pb4sc