Julie,The yard gully is the overflow point in the event of a sewer choke. Identified by the grate in the top and usually outside the kitchen. It should finish above ground level, to stop stormwater getting in, and 150mm below floor level, to stop sewage coming up through the bathroom floor grate. If it is higher than floor level guess where the sewer will overflow if you have a sewer choke? Yes inside your house. So have it fixed as soon as possible. As far as cost only a site inspection by a plumber can determine that.: I have been told to lower my existing yard gully (or : relocate it) to achieve 150 mm below floor level. : What is a yard gully? Approx. how much would it cost to : lower/relocate it?: Thanks, : Julie. : 2/11/98