Dear Adele,
One of the points to bear in mind about reducing flush volumes is
that once the solids have been flushed, they still need to be
transported down the sewer system to the treatment works. Reducing
the flush volume may cause problems with this solid transport,
especially for long drain runs, with few connections. It is therefore
important that any flush wave is as concentrated as possible (high
peak flow, short duration) when it leaves the WC, also that the solid
is moved as early in the flush as possible, to maximise the transport
distance.
Roland's earlier comments about the legislation preventing the use of
the siphon mechanism in the UK may soon be out of date, as the Water
Regulations are likely to allow dual flush WCs, and non-siphonic
flushing mechanisms in the UK.
Kim Littlewood
Water Research Centre
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