into the center of the bottom of a plastic bottle. cut two ice bags so that they are about one inch in length, and then use rubber bands to tie an ice bag to each end of a y-tube. place the y-tube into the opening at the bottom of the plastic bottle. use modeling clay to fix the y-tube in place so that no air can get in or out. cut a rubber balloon in half. stretch the top part of the balloon with the air tube under the bottle and use rubber bands to fix it into position. tie a piece of string to the air tube of the 