I want to add a 1/2 bathroom in my home which is on a slab foundation. The new bathroom would share a common wall with the original bathroom. The toilet and sink would be back to back with the original bathroom toilet and sink. What is the best way to accomplish this with the least amount of tear up of wall and floor. Thanks Mickey

If you open the wall you will see the drain and vent stack for the existing bath, right behind the toilet. You will need to break out the floor for the new toilet drain line to connect to the existing drain and your sink can be tapped into the drain above the floor. Is this drain pipe also the vent stack all the way to the roof line?