Professional window washers often use a specialized cleaning solution comprising a mix of water and mild detergent or a commercial window cleaning product. These solutions are formulated to cut through dirt, grime, and grease without leaving streaks or residue on the glass. Additionally, some window cleaning companies may have their own proprietary cleaning solutions tailored to their specific needs and preferences. Ultimately, the choice of cleaner depends on factors like the type of dirt, the condition of the windows, and environmental considerations, ensuring a streak-free shine on windows of commercial buildings, skyscrapers, and residential properties alike.