You do not necessarily need to buy the Bosch detergent concentrate to use with this window vacuum cleaner. The manual advises using detergents designed for window vacuum machines and for best results recommends Bosch glass detergent concentrate. However, you can use any glass cleaning liquids that are suitable for window vacuum machines, provided they do not contain undiluted acids, acetone, solvents, flammable liquids, or hot/boiling water, as these can damage the machine or surfaces. It is also recommended to test any detergent on an inconspicuous area first to ensure compatibility and avoid damage or discoloration.