My first floor bathroom toilet fills to the brim when flushed then empties slowly. The other (ground floor) toilet seems to empty fine. The soil stack therefore I presume is blocked. It is cast iron with no access covers. I have removed the toilet pan and rodded down the stack while standing in the bathroom but the blockage fails to clear. My next move will be to cut the iron soil pipe eighteen inches above ground level and rod from here with a view to repairing the iron pipe with a rubber ring or replacing the entire stack with plastic. Any ideas would be appreciated.