Elbow Grease – Cannot be bottled or purchased, must come directly from the elbow of the person using it. Varying degrees of pain may be involved.
Toilet bowl – The part of the toilet that looks like a bowl. Fairly self-explanatory, but a hilarious mental picture to a 6 year old boy.
Unwieldy – Difficult to carry due to shape, size, etc. Used in a sentence: The Oreck vacuum cleaner only weighs 8 pounds, but it is unwieldy to a boy who is not as tall as the vacuum cleaner.