OK I looked at the pipe a bit closer.
I turned on the upstairs sink, and it's draining down the pipe labeled below. The pipe that the washing machine is draining into is the one that's a couple feet closer to us.
In this picture, you see the drain pipe for the upstairs sink on the left. The pipe on the right is the one that's hooked to the laundry machine drain. I would ASSume that this is also the vent for the sink? I looked in the attic, and there is a pipe coming up in this same area tied over into another pipe (vent) going up through the roof. This leads me to believe this pipe is purely vent (no drain coming from above).
With that said, what is the proper way to set up the washer and sink traps/vents? Thank you!