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of the house. The unstopping of the raking arm is not the only
cause of the reversal of the air currents through the inlet pipe,
but we are not now concerned with the other causes. There is no
doubt as to the cause of the unstopping of the raking arm in the
majority of these 225 cases. The raking arm was unstopped by
the pressure of air in the sewer, and the cap falling into the mouth
of the intercepting trap, caused an accumulation of sewage in the
manhole. There are many types of traps now on the market in
which a stoppage cannot take place from this cause.
In addition to the 58 traps stopped by the cap of the raking
arm, in 66 other instances the interceptors were obstructed, and an
accumulation of sewage occurred in the inspection chamber. In the
case of some of these, the obstruction was due to the actions of
the occupiers of the house, but in the majority of instances it was
due, either to an inherent defect in the trap, or to a faulty construction.
But apart from an actual obstruction, the 6-inch intercepting
traps were generally foul. In hardly a single instance did we find
a self-cleansing 6-inch trap, and it is almost impossible for a 2 gallon
or even a 2½ gallon flush to scour a 6 inch trap.
Under present conditions, most of the 6 inch intercepting
traps are miniature cesspools in the immediate vicinity of a house.
They hold over a gallon of decomposing sewage.
The number of traps inspected is admittedly small, but the
results obtained are in accordance with the experience gained in
the routine work of the district. It may also be mentioned that
these defects are not peculiar to old property, but most of the drains
inspected were those of houses erected within recent years, and may
I think, be taken as a fair criterion of what obtains throughout the
district. The results also coincide with those obtained in other
districts where a systematic inspection of these traps has been carried
out. For instance, in a neighbouring district 6,745 intercepting
traps were inspected. Of these 288 were choked, and in 654 instances
the cap of the raking arm had fallen into the inspection
chamber.