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sufficient means of access (e.g., chambers, inspection
pipes, &c.) supplied to every portion of the drainage
system, which must be thoroughly ventilated. With
more than six houses on the combined system, the
main combined drain must be treated as a sewer, and
dealt with (as to ventilation, fall, means of access, &c.),
accordingly.
Finally, where a single house can be drained separately,
with the drains outside, a combined system is neither
necessary nor advisable; but rather than have a drain
under and through each house, it is better to have a
combined system, with a main combined drain passing
through and under one house (provided no open
passage-way is available), thereby minimising in proportion
the danger, or chance of accident, from leaky
drains and joints due to settlements, &c.
To sum up, it is impossible to lay down any hard and
fast rule; each plan must be taken and considered
on its own merits and approved:—
1. As a Combined System.—If by so doing the
drainage scheme is simplified as much as possible,
and the drains kept outside, or (a rare necessity) even
taken through and under one house, instead of through
and under several.
2. With separate drain to each house.—Provided
that this can be effected with drains outside.
Out of 35 Metropolitan Districts communicated with, only
five do not allow or approve of combined drainage—two
in connection with new, and three in connection with
new or old, buildings. The other 30 Districts allow and
approve of combined drainage—
(a) Where there is no obvious disadvantage (2 Districts).
(b) In certain cases (12 Districts).