I have a 4" cast iron vent on the end of a line just after the toilet. I am wanting to install a cleanout to the outside brick wall approx. 3' away. First, is it okay to do this? Second, any height requirements off the slab. Third what's the easiest way, cut a hole in the existing cast and put on a saddle or pull the cast stack out and reinstall with PVC or what. If the easiest is to cut a hole, how do I cut the hole, the sheetrock is off on one side of the wall only? Fourth, what would be the size I should use, I want to use PVC?