- two dirty bottles, one with a lid
- soapy water
First take the bottle with the lid on it, show it to the class and say: See this bottle is really dirty.
Put it in the soapy water and wash it and then rinse it, and wipe it dry. Show it to the class and ask: Why isn't it clean? (Student choice.)
Now show the second bottle, the one without a lid and say: See, it is very dirty, but I'm only going to wash the inside. That is my main goal, just the inside.
Put it into the soapy water and scrub the inside very thoroughly, then rinse and wipe the inside dry with a paper towel. (Don't worry about getting the outside wet--it's suppose to happen.)