It works, but does not seem to be drawing detergent solution. Is there a switch or a knob that I am not aware need and needed to turn on to draw detergent?
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You will need to use the black (soap) spray tip that came with your pressure washer. It allows the valve to open so the rushing water picks up detergent & adds it to the water flow by siphon action.
Your pressure washer-safe detergent needs to have a thin consistency, more like water than dish soap. Otherwise the water won't be able to pick it up. We say "pressure washer-safe" since the soap travels through your pump with the water- caustic soap or chemicals will damage the seals in the pump and void the warranty.
You can click on this link to see the Pressure Washer Safe Detergents that we sell; they may also be available in your area. Some can be used right out of the bottle, and some will need to be diluted first- please follow the manufacturer's instructions.