A dispenser of washing agents for a dishwasher has a body with a reservoir configured for containing a total amount of a liquid substance sufficient for performing a number of cycles of operation of the dishwasher. The reservoir has a charging passage that can be engaged by a removable plug, and the dispenser has a system for dosage of the liquid substance contained in the reservoir. The plug is configured for co-operating with an adjustment element belonging to the dosage system when the plug itself is at least partially inserted in the charging passage, particularly in such a way that a movement of rotation manually imparted on the plug will bring about a movement of rotation of the adjustment element.