We purchase the CST743S without noticing one important detail. Our new toilet will be installed in our master bathroom back to back to the guest bathroom. While reading up on the installation instructions it mentions that the only means possible of doing this is if there is a "WYE". fitting in the standpipe. Unfortunately our standpipe that is cast iron, has a double sanitary tee or cross. Will I need to tear out the drywall to install the proper connection or can I get by with what I have? Thank you