This is a recall from previous snake services. Customer stated that periodically the toilet would back up. During my investigation, I had both bathrooms running all fixtures at the same time with no back up. I proceeded to camera existing vent line through roof with no obstructions. The existing main vent line for the master bath is a 2 inch cast-iron pipe, which could periodically restrict airflow for proper drain drainage. This line should be 3 inch. At this time, main sewer cleanout could not be located and homeowner does not know where it is. After our conversation on the phone, he stated that he is OK if everything is flushing fine at the moment.