I am replacing the sink in my kitchen and I can't figure out how to attach the sink drain to the drain pipe itself. On the old sink it looked like the drainpipe and drain were glued together or something but I couldn't get it apart. Coming out of the wall I have 2" abs which reduces to 1.5" abs. Should I just use a peice of pvc or metal pipe from the p-trap to the drain? Or am I just missing some key step? I have looked in a few plumbing books but they do not sufficiently explain how to do it with abs.