Settling tank

A sewage settling or septic tank is divided by at least one partition 3, 4 into chambers 7, 8, 9 which act in series on liquid flowing from inlet 12 to outlet 13. The chambers communicate by restricted openings 10, 11 to allow liquid flow while retaining solids mainly in chamber 7. Sludge is periodically pumped from chamber 7 by a pipe lowered through passage 4a, which an upward extension of partition 4 and extends above the liquid level 16. During such desludging, flap valves 20 open to allow sludge from chamber 9 to fall into chamber 7. Openings 11 between chambers 8 and 9 are confined to the region opposite outlet 13. Valve 20 (Figs. 3, 4) comprises a moulded rubber cup having a slit (25) which is constrained to a closed position when the mouth of the cup is engaged with a hole through a flat wall.