How do you make a vortex?

how do u make a vortex?well u get two bottles big ones .then u get tape foil and food coloring.u put some water in one bottle.then u get a washer and put it on the bottles u also put the foil on it.then u put the food coloring in the water and u stick both of the water bottles together and stick it wit tape togethr thn u swril it around and flip it over and wait till all the water rushes down then u flip it back over and u will c a vortex