Abstract: A method of filtering liquid media comprises directing liquid to be filtered into a vessel under pressure and draining filtered liquid media from the filtration vessel. In backwash mode liquid is forced through filter media effecting rotating flow and fluidisation of the filter media, and in normal operation liquid present in the vessel above the filter media is caused to undergo rotating flow about the vessel. The drain arrangement includes a plurality of radially extending limbs configured to act as backwash liquid distribution means in backwash mode or filtered liquid collection means in normal filter mode. In backwash mode, liquid is distributed in a direction transverse to the longitudinal direction of the respective limbs; and/or the majority of the limbs direct water either clockwise or anticlockwise.