I am moving my laundry from the basement to the 1st floor. There is a 2" drain line from the kitchen sink near by so I can run the new washer drain into that. Should I use 1 1/2" or 2" PVC from the washer to the existing 2" PVC? Also, where is the best place to put the trap? The area below is unfinished so I do have options.
Thank You

Since the sink drain's 18" off the floor you stand pipe wiill be a short one.,( make the stand pipe a few inches over the flood rim of the washer. You will have to make the system a closed one by attaching the washer to the stand pipe with one of these connectors,(see image) or you could simply duct tape the hose to the pipe.
It will go down like this. First the stand pipe (2" all the way) into a "P" trap. From there it would be nice if you could 45 over to a 2" wye cut into the drain. Next best is to go directly into a 2" combination eighth bend and wye cut into the drain. This job won't be inspected will it?
Good luck, Tom