Roscoe writes: “This is the only valve that I’ve found which allows you to spray soap concentrate at high pressure through any pressure washer with any wand or tip. It turns an affordable pressure washer from the home center into a machine that feels like the wand at the car wash. Every pressure washer manufacturer should include this with their unit.”
This looks way better than the little bin on my crappy electric power washer. The one pictured above comes from Northern Tool, and sells for $30.
Upstream Pressure Washer Soap Injector [Northern Tool]