Unless you convert yours to an upstream injector, you'll need a detergent made to work with downstream injectors. Again, the simplest way to do this is by getting Ryobi brand detergents and foams.

Package: Complete kit with siphon hose + 3 filters. Upgrade your pressure washer with the soap injector system for pro-grade cleaning performance. Dimension: 10 Feet (ID 0.28" / OD 0.35") is long ...

Unless you convert yours to an upstream injector, you'll need a detergent made to work with downstream injectors. Again, the simplest way to do this is by getting Ryobi brand detergents and foams.