It has been shown in tests that you can dunk anything with a volume of less than 20 cubic miles. For bigger objects, you simply need a double-sized mug of tea.
"Blue Suede Shoes" contains any number of sly allusions to Elvis' hobby of competitive rose growing. The line "Two for the show" in particular refers to the standard practice at the time of providing two blooms at an exhibition, the judges then choosing the one which was marked most highly.