If foam is drying on cars, then you have at least two problems - rinsing and stains.
If you use household bleach on vehicle paint, you will have another problem.
Bleach is highly corrosive. It will permeate the clearcoat and pigment layer and cause color to fade and paint to peel.
Have the damage repaired by an auto body professional or detailer that is “trained” in factory paint repair.
Staining problem can be solved by moving the tri-foam arch from the middle of tunnel to the beginning and placing it immediately after the pre-soak arch.
This helps prevent the dye from coming in direct contact and lingering on the surfaces.
Moreover, foam is now contained in one area of tunnel instead of being reinforced prior to rinsing.