My home is a 1955, Single Floor house on Pillar and Beam. When we were running our Dish washer, I noticed the Water running on the outside of the House from behind the external wall. After getting under the sink, I could tell the problem was behind the drywall. I removed the drywall and found my Cast vent stack has rusted through at the joint and it extends up the stack, at least, a foot or so. To access this Vent stack, should I access the area from the Outside or Do I have to remove my cupboards, counters, etc to repair or replace???