A liquid chemical dispenser for an irrigation system comprises a removable supply container for the chemical which, in a first embodiment, comprises a valve for preventing spillage of the chemical during attachment of the container to the dispenser. This feature allows the container to be mounted in an inverted position on the dispenser without loss of its contents. In a second embodiment, the chemical container comprises a membrane which is pierced by a dip tube when the container is attached to the dispenser. A section of the dip tube produces an annular vent passage in the membrane around the dip tube to provide vacuum relief. The configuration of the containers substantially reduces the chance of inadvertent contact with the contents and the simple design permits the containers to be disposable.