Dear Suresh
In bathroom where waste water is goes through floor trap which is connected with 4'' or 5'' dia PVC OR CI pipes to sewer line or open drain as the case may be. After fixing the floor trap we provide gratings on the floor trap which help in to provide barrier for entering the rats and droping any material inside bath room which may cause chowking of function of pipe. One other benifit of providing gratting on the floor trap that there is no any chance of baby foot in to the floor trap.