Can anyone give me some ideas on the best way of replacing a clay gully with a plastic gully. Currently i have a cast iron down pipe which is connected to a hopper at the top, this carries waste from my bath,basin and condenser pipe down to a exposed clay channel , I also have the kitchen sink waste pipe which discharges on the channel and then runs into into a square clay gully. I want to replace this with a plastic gully and, at the same time get rid of the clay channel. Whats the best way in replacing this.