Abstract: Dispensing systems for dispensing one or more materials into a fluid flow conduit, during the conveyance of fluid through the conduit are configured to connect to a fluid conduit, such as a standard pipe of a shower arm and dispense a material into the water flow in the shower arm. The system includes a first tube member having a restrictor flow passage to provide a pressure differential, as fluid flows through the tube member. The pressure differential created within the restrictor passage by the fluid flow is communicated to a flask, to provide a pressure differential between the interior and the exterior of a flexible container within the flask. The pressure differential causes material within the flexible container to be drawn out and conveyed to the fluid flowing through the tube member. The flask may be connected to the first tube member, through an extension portion that is rotatable around the first tube member for convenient positioning.