My current bathroom is on the ground floor. The kitchen and sink water discharge into a gulley. The toilet discharges into the drains through the floor. Outside the bathroom is a cast iron soil stack upto roof height which I assume is a vent? I am putting in an ensuite upstairs and have only thought about drains at last minute!!! foolish I know. The soil stack is about 15 feet further along wall from where upstairs toilet will be. I assume I can tee into existing soil vent lower down wall but wondered how you cut into cast iron. everything in wickes I have looked at is plastic. Or is it better to just replace the cast iron with all plastic from the ground up? I assume I can put the bath waste into the same point higher up the stack rather than taking it into a gulley at ground level? All advice is much appreciated.