Undoubtedly, the plastic siphon for washbasin much better than cast iron. But the trouble is that they are not interchangeable. Throwing worn-out iron and putting plastic, we have something to fill the annular gap, as each of the pipe under the old syphon has an internal Ø 72 mm, and outer diameter of plastic pipe is only 40 mm. Propose to put into the gap washer Ø 72X40 and a thickness of 20 mm, cut from sheet rubber. The connection is quite tight and the unit is easily disassembled for cleaning sewers.
A. LEVITSKY, Kiev