If plumbing gets clogged due to items dropped in the toilet (toys, brushes, diapers, napkins, any personal items), clogged or misused garbage disposal, the cost of the plumber will be your responsibility (minimum $150). This is not considered equipment failure and you should do everything you can to handle these issues by yourself. Unless the contractor can prove it was not caused by you (i.e. roots in the system, pipe collapsed, septic tank backup), we assume it was caused by people, not by a defect of the property. Clogged plumbing is your responsibility.