Plug (1) comprises a sealing part (2) facing at least one sealing surface or seal (3) and resting directly on the edge (4) of an outlet (5) of a sink (6), container, etc. An at least partly open carrier (8) provided on the outlet side contains a substance (9) that is gradually used up in water. In the region of and/or below the outlet the carrier has at least one opening (12, 12') for a liquid/substance exchange between the space (14) externally surrounding the carrier and its interior. Preferred Features: The carrier is a removable and fillable container (8').
