It is basically a siphon type sprayer. As the air passes by the water syphon tube it draws the water up the tube.
You can get one of these from Harbor Freight ready made just need air and a water supply. $8.99!
It comes with the syphon tube. To use with a prop controller or relay; keep the engine cleaner's trigger open with a zip tie, hose clamp, etc. Activate the spray by triggering an air solenoid with the controller/relay.