Does my SPX3001 pressure washer have a downstream or upstream detergent injector?

Your Sun Joe Pressure Joe SPX3001 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.