Can I put any car shampoo in a foam cannon?

Use a shampoo formulated for foam cannons: ordinary car wash liquid produces thin foam that runs off before it has done anything.

Foam works by dwelling. A product designed for a bucket is designed to be used immediately, and it lacks the surfactant package that makes foam cling for minutes.

Adjust the cannon’s dilution rather than adding more product: thicker is not automatically better, and very thick foam can be harder to rinse fully.

Never use washing-up liquid — it strips wax and protective coatings along with the dirt.