Abstract: An apparatus for controlling liquid flow from a holding vessel to a discharge line wherein insoluble material received into the vessel with liquid is intended to be retained in the vessel. The apparatus comprises wall means within which an interior cavity is defined for connection to the discharge line at a location below the surface of liquid in the vessel, apertures spaced along the wall means for admitting liquid from the vessel into the cavity, wall elements between the apertures providing inclined confronting ramps between which pockets are provided such that the liquid therein is relatively quiescent to facilitate movement upwardly of buoyant components of the insoluble material to be deflected by the superior ramp towards the top of the vessel and movement downwardly of non-buoyant components of the insoluble material to be deflected by the inferior ramp towards the bottom of the vessel.