I bought a second tube holder (the black plastic thing referred to above) so I can easily change tubes for the 2 step Audio Intelligent fluids. They suggest 2 tubes and 2 brushed to avoid contamination of the different types of fluid, 1 being enzymatic and 2 removing the enzyme fluid. They even have a step 3 that is just pure water, but that is too many steps for me and may not yield and better results.
