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Unless the pumping arrangement is automatic in action, nuisance is
apt to arise, as in one case in which a large quantity of fluid was
pumped into the sewer at a time, causing thereby a considerable escape
of effluvium from the ventilating grids in the roadway. This has been
remedied by—
(a) Pumping at night when the sewer is practically empty, so
as to avoid creating pressure of gas ;
(b) Lengthening the suction pipes of the pumps so as to reach
the bottom of the tank, and grading the bottom of the tank to
obtain scouring action, ensuring that when the pumping ceases no
liquid is left in the tank to become offensive; and
(c) Adding chemicals at frequent intervals.
Intercepting Traps to Drains.—A Departmental Committee was
appointed by the Local Government Board in 1908, to inquire as to the
usefulness or the reverse of intercepting traps to house drains. The
committee has now issued a report, from which it appears that complaints
which have been made, have been due in great measure to the
use of unsuitable forms, and to want of supervision in securing that
such traps are properly fixed, which they admit is by no means a simple
proceeding. (In Westminster, the Sanitary Inspectors examine every
intercepting trap when it is being put in, with the result that subsequent
obstruction in the trap is of very rare occurrence.) The Committee
think that under certain circumstances the use of this trap need
not be insisted upon, but the requirements considered necessary to
compensate for its absence would raise the cost of a drainage scheme for
a house by 10 to 20 per cent. Iron drains with lead joints would be
essential, and as both sewer and drain would be ventilated through the
soil pipe, very great care would have to be exercised to keep the vent
pipes away from windows, chimneys, &c. The Committee suggest that
the intercepting trap is susceptible of improvement as to size and
shape (the trap should be 1 inch less in diameter than the drain discharging
into it), the open channel drain on the floor of the inspection
chamber should be abolished, and a closed drain provided, with a
screwed-down removable cover; the fresh air inlet may frequently be
dispensed with without practical disadvantage.
It had been contended by some engineers that if intercepting traps
were done away with, sewers would be better ventilated by means ot
the soil pipes of each house. The Committee is of opinion that the
necessity for ventilation of sewers has been exaggerated, and that free
ventilation is unnecessary and impracticable. It is pointed out that in
all cases before men enter the sewers special precautions should be
taken, and that it is dangerous to rely for safety on ventilation. The
prevention of nuisance from smell renders it necessary that any openings