Gravity drainage
The Illustrated Guide to Hot and Cold Water Services (BG 33/2014), written by Reginald Brown and published by BSRIA in 2014, it states: ‘In a gravity drainage system all horizontal pipes are laid to a slight fall in the direction of the soil stack or sewer connection. If the fall is too little then the pipe will not drain efficiently. If the fall is too great and too long then there is a possibility of the suction created by the discharge removing the water seal. The optimum fall for different situations is as recommended in Approved Document H.’
See also: Pumped drainage.
--BSRIA
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