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65
It will be seen from the above summary that several of the
blockages were caused by the presence of small accumulations of
cement or concrete in the intercepting traps, which the workmen
had neglected to remove at the time the drains were laid. In addition
to this the foul condition of a number of the interceptors, and their
consequent tendency to become choked, was, without doubt, largely
due to their unnecessarily large size and the careless manner in which
they had been fixed. It would appear that in many instances no
precaution had been taken to ensure that the traps were correctly
set as regards "seal." No less than 22 of those examined were found
to have a seal varying from four inches to six inches, that of 59 others
varied from three inches to four inches, and the seal of the remaining
66 ranged from one and a half inches to three inches.
It will be seen that in four instances the "cap" on the cleansing
arm had been displaced. In this connection we do not consider that
an intercepting trap should be passed by the inspecting officer unless
some precaution is taken to prevent this mishap. Good locking
"caps" are easily obtainable, which are capable of removal from the
ground surface, and in cases where expense is a matter of consideration,
the practice of the health department here is to have the usual
stoneware stopper removed and a slate stopper fixed in lieu thereof,
with a fillet of Portland cement round its outer edge. The centre of
the slate is thus left bare, and can easily be broken if a blockage
should occur.
In respect to size, the unsuitability of six inch traps for houses
which have only a small number of w.c.'s, baths, sinks, etc., was
clearly demonstrated in a large percentage of cases, the collection
of grease and scum about the inlets of the traps having reduced the
water way to about four inches in diameter. It might be here
mentioned that many 6-in. traps hold as much as 2 or 3 gallons of
water, whereas we found that a six inch trap of a good type set with
a 2J-in. seal only held 1\ pints. (By way of comparison a good type
of four inch interceptor with a 2-in seal will retain 4 to 5 pints of
water.)
The usual two-gallon flush from the w.c. flushing apparatus is
not sufficient to properly change the contents of a good type of six
inch trap, and it is, therefore, not surprising that the unnecessarily
large traps, especially when carelessly fixed, are liable to become
choked. The cleanly condition of the 4-in. traps which came under
observation was very marked in comparision with the six inch traps,