Seal the ends of a plastic drinking straw.
Take a paper napkin and tear a three inch square from it.  Wad that up and get it wet.  Make a ball of the square and jam that into the end of the straw.
Hold one end in the fire provided by a small candle.  Heat it but do not let it catch fire.  Remove from the heat and squish with a pliers.  The plastic should be soft enough to melt together.