James Bartlett, 1911 Encyclopædia Britannica (1911)
“ When the gradient is slight, and the dry-weather flow very small, occasional flushing must be resorted to. Flap valves or sliding pen stocks are introduced at manholes; by closing these for a short time sewage (or clean water introduced for the purpose) is dammed up behind the valve either in higher parts of the sewer or in a special flushing chamber, and is then allowed to advance with a rush. Many self-acting arrangements for flushing have been devised which act by allowing a continuous stream of comparatively small volume to accumulate in a tank that discharges itself suddenly when full. ”
