The inverted bottle can be held by hand or placed in an iron ring on a ring stand for support. Ask one of your students to try inserting a colored match stick into the paper punch hole. If they are careful, it should float up with little or no loss of water. It is a good idea to have a catch pan under the bottle to take care of unsuccessful attempts. If problems occur, try using different types of plastic for the disc.
Some teachers use the plastic from the tops of fast food drink cups.
Obtain plastic berry baskets from the produce section of your grocery store. The ones that work best have square rather than diamond shaped holes in the bottom. In a large beaker or fish tank demonstrate to your students that the basket will float if placed carefully on the surface. Push the basket under to show that it sinks when not supported by surface tension. Have one of your students try to float the basket, they will not be able to easily float the basket because it will be wet.