Does my SPX3000 pressure washer have a downstream or upstream detergent injector? Your Sun Joe Pressure Joe SPX3000 has a downstream chemical injector, installed on the outlet (discharge) side of the pump, that applies detergent with the dedicated soap nozzle. The advantage of the downstream injector is that the chemicals cannot cause damage to the pump system. In upstream injectors, the chemicals run through the pump, causing the pump seals to wear out. Related articles Why is there no detergent coming out? Can I use disinfectants as detergent with my pressure washer? How do I assemble my SPX3000® Pressure Washer? What size screws do I need to assemble my SPX3000®? Does my SPX3001 pressure washer have a downstream or upstream detergent injector?