Workers manually do the checking, by entering into manholes. They find it difficult to carry anything that they can record their observations on. They have to come outside and fill up forms, which are then passed on to repair crews.There is no way that a supervisor can be sure that a worker has done his job. There is no record of him having actually entered the sewer. There is just a paper record which the worker himself creates. The sewer being not exactly a pleasant place to enter, makes it even more likely that the worker may not actually enter a sewer but only make a dummy paper record of entry.