A siphon nozzle is a special attachment for a pressure washer that allows an additional substance to be drawn in and mixed into the water jet. It operates on the Venturi effect principle, where rapidly flowing water in the nozzle creates a vacuum. This vacuum then draws in material, such as abrasive sand or cleaning agent, from an attached hose and mixes it with the water. Its main application is in so-called "wet sandblasting," where the mixture of water and abrasive effectively removes rust, old coatings, or dirt from solid surfaces. It can also be used to draw in chemical cleaning agents or foam, which protects the internal pump of the washer from damage because the chemicals do not pass directly through it.