A liquid filter, suitable for the lubricating oil of an internal combustion engine, having a cartridge installation opening 15 which faces substantially downward, a positively guided oil drain 28 is proposed for draining oil from the filter when the filter cartridge is changed. The positive guidance is effected by a valve stem 29 which is connected directly or indirectly to the housing by a support tube 22. It opens a gasketed drain opening which can be connected to a hose 35 in order to assure drainage of oil, for example, to a separate oil collecting vessel. The drain opening is automatically opened by unscrewing the screw-on cover 11. No other drain plug or the like needs to be opened. This filter is especially suited for installation in confined spaces since the oil can be drained in a reliable manner.