Interceptor traps can be found in many Irish properties constructed to up the 1970’s. It is normally located at the final chamber nearest the public sewer and may be provided with a fresh air inlet.
The interceptor trap, or ‘winser trap’ as defined by the Water Research Centre, is a development of the buchan trap; the key difference being that the trap was now constructed in a chamber and access was provided both upstream and downstream. The original buchan trap could only be rodded from ground level through a rodding eye to clean the trap itself. Access to the trap would be provided by an inspection chamber upstream.
Buchan traps were originally used in Victorian times to prevent sewer gases entering the atmosphere or dwelling using a water seal. It was patented by a Scottish sanitary engineer, W.P Buchan, in 1875. Another function of the trap was to prevent (or rather limit) the ingress of our furry friends. However, as the winser trap was susceptible to blockages, many householders removed the stopper to the rodding eye allowing easy access for rats.
Winser and buchan traps are no longer installed due to much improvement in the design and construction of drainage systems, particularly from a ventilation point. Such traps can be a common cause of blockages so it’s worth while keeping an eye on it from time to time.