Plug the pressure washer into a power outlet with GFCI protection. This stands for ground fault circuit interrupter. If you need an extension cord, only use 12- or 14-gauge cords.
Adjust the spray nozzle of the pressure washer. Lighter duty models tend to come with one adjustable spray nozzle. A more concentrated spray should be used for stains and heavily contaminated areas, while a finer spray can be used for general cleaning of the interior space. The lower the degree of the nozzle, the more concentrated the spray will be.
Fill the reservoir area with detergent and connect the pressure washer inlet to your garden hose for the water supply.
Switch to water mode and rinse down the area you're cleaning thoroughly. Switch the pressure washer to detergent mode to clean the surfaces. Detergent can help get off tough stains or disinfect interior spaces, such as after floor damage or a sewage backup. Switch back to water mode to rinse the surfaces.
Dry the interior surfaces. Use a squeegee to remove water runoff if there is a drain nearby, such as in a garage or basement. Otherwise, open windows and remove standing water with a mop. Then, use a wet/dry vacuum to extract all remaining liquid from the interior surfaces.