Bell trap

A bell trap is an older style of gully trap in which a metal or stoneware bell sits inverted in a water pocket inside the gully chamber, creating the water seal. Wastewater flows around and under the rim of the bell before continuing to the drain. Bell traps were widely fitted in Victorian and early 20th century London properties but have largely been superseded by more reliable P-trap and back-inlet designs. The bell can be lifted out for cleaning, although the seal is more vulnerable to evaporation and disturbance than modern alternatives. Where bell traps are still found, they are sometimes replaced during drainage refurbishment to improve odour control and provide better access for rodding. They are not generally specified in new UK installations.