I want to replace existing plastic toilet with porcelain. The toilets I have seen will not fit because of the box/chase along the wall behind the toilet. The box/chase is 4 1/2" deep and 9" in height. I would like to know what is in that box/chase and if I can modify it to make the toilet fit? I know there is one 1/2" pex water supply line for the toilet. Thanks! I would appreciate any information. Randy