Remove the hose that comes attached to the garden sprayer.
Attach a quick-release valve to the garden sprayer with five-minute epoxy.
Attach the vinyl tube to the quick-release valve. If the valve has a nipple, simply push the tube onto it. Otherwise use epoxy or a zip-tie.
Seal the other end of the tube shut with epoxy.
Cut a small diamond shape into the tube 3 inches below the sealed end.
Fill the sprayer's tank with fake blood. If it is thick, thin it a bit with water.
Close the quick-release valve.
Pump the garden sprayer 30 to 40 times to pressurize it.
Duct tape the end of the tubing to the actor's skin. The diamond hole should be positioned facing out through a small hole in the clothing.
Open the quick-release valve to allow all of the pressure (and blood) to be released through the diamond hole.