Want to add a sink to my laundry room so I need hot and cold water and a drain. How do I splice in to the existing ones? I know I remove some drywall to get to the area. Now, do I drill holes through the studs for new drain and water lines, or notch out the edge of studs for the drain line? Do I need to put the drain line at an angle so gravity helps? Any other thoughts appreciated. Thanks.

A lot depends on the piping that's there now. You'll need to add a tee in the vent for the washing machine. It needs to be dry above the tee, meaning that the washing machine drain needs to tee into the vent below the tee you add. Drill the studs in the center, each hole a 1/4" lower than the last hole you drilled. You'll need to add stud guards (metal Plates) to the face of each stud you drill so that a nail won't penetrate the pipe.

I would suggest hire a licensed plumber. Get a few bids.

if you post a photo of what you have, more specific information can be given. right now answers are just guesses..

I agree.