In the process of fitting a new bath and when we exposed the soil pipe, which is cast iron, the 40mm solvent pipe coming off the bath its terminating into a branch on the soil stack which is about 50-55mm in diameter. All the previous installer has done is shove the bath waste into that branch and siliconed it up, but its now leaking like crazy. Anyone any ideas how you'd connect 40mm solvent pipe to 50-55mm cast soil pipe?