as you said, if the distance between the sewer crossing and the toilet sewer is only 3 cm, you can expand the main sewer crossing by 3 cm in the direction of the toilet. (Pay attention to taking measures to prevent debris from falling into the pipeline when expanding the sewer.) Use the "plastic mud plugging agent" to repair and reshape the pipe mouth and prevent the pipe mouth from leaking. Plastic mud dries quickly, and it only takes half an hour to slow down. Please refer to the product description of the "plastic steel mud plugging agent" for the usage method and scope of use.