You will need:
A recycled water bottle or softdrink bottle
An old sock
A rubber band or duct tape
Dishwashing liquid
Water
A basin
Scissors
Food colouring (optional)
Method:
Carefully cut the bottom off your bottle.
Place an old sock over the end of the bottle and secure with rubber bands or duct tape.
Dip the sock end into a basin of soapy water (you can add food colouring to the soap and water mix if you wish).
Blow!
Credits to housingaforest.com blog for the great pics of this fun outdoor activity.