Underground Drainage Systems

A 110mm foul drain taking the discharge of less than 1 l/s should be laid at a 1:40 (25mm per metre) fall. A foul drain taking the discharge from a minimum of one WC can be laid at 1:80 (12.5mm per metre). Gullies incorporating in foul water or combined drainage systems must have a 50mm minimum water seal. The table below is taken from BS EN 752 ................
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