A liquid filter including a filter housing, a ring filter insert and a cover. The housing bottom contains an outlet for emptying the housing when the filter insert is removed. The filter insert includes a filter material body surrounded by front panels. A blocking element for the outlet is arranged on one front panel, and positioning elements are provided on the filter insert and on the housing. The positioning elements include an inclined plane and an engaging radially protruding nose. The inclined plane is arranged on one and the nose is arranged on the other of the filter housing part and the ring filter insert. When the ring filter insert is rotated relative to the filter housing, the inclined plane and the nose are moved in relation to each other such that they slide along each other and engage the blocking element with the outlet.