Apparatus (10) for collecting solids selling on the bottom of a liquid reservoir and/or floating solids, the apparatus (10) having a hollow suction head (23) and at least one outlet duct (26) extending from the suction head (23). Air can be supplied to the suction head (23) to create a suction pressure in the suction head (23) to cause settling solids beneath the suction head (23) to pass along the outlet duct or ducts (26). The suction head (23) may be connected to a collector (11) which is provided with a float (21) to support the collector (11) at the surface of the liquid, and the outlet duct or ducts (26) are connected to the collector (11) which collects the solids. The collector (11) may also have an inlet to collect floating solids.