There are essentially two ways you can add soap to a pressure washer: upstream or downstream. Both have advantages and disadvantages. Whatever way you choose, either is usually much more efficient than using soap to clean without adding it to the pressure washer. Knowing specifically how to add soap to a pressure washer, whether upstream (before the water pump) or downstream (after the water pump), saves time and labor, not to mention money if it is a commercial endeavor.
Choose to install an upstream (before the water pump) chemical injector kit so that soap is added to the pressure washer and onto whatever you're cleaning under high pressure. Choose to install a downstream (after the water pump) chemical injector kit so that the soap is added to the pressure washer and onto whatever you're cleaning under low pressure.
Install one of these two types of chemical injector kits, if one isn't already installed. Follow instructions provided by the manufacturer, or have it installed by a professional, if necessary.
Attach the weighted strainer (filter) to the siphon tube. Slide the other end of the siphon tube onto the hose barb on the chemical injector.
Place the bucket near to the pressure washer. Don your protective eyewear and protective gloves.
Fill the bucket with appropriate cleaning solution and drop the weighted strainer into the bucket.
Connect a water hose to the water inlet valve on the pressure washer. Connect the other end of the hose to an adequate water source.
Connect the pressure washer hoses, pressure washer gun and wand, or lance.
Turn on the water and start the pressure washer.
Depress the pressure washer gun trigger, allowing water to flow throughout the system. The force of the water pressure will draw the cleaning solution up through the siphon tube, mixing it with the water coursing throughout the pressure washer.