Meaning a girl will fuck really hard. The “dunny” is Australian slang for a toilet/bathroom and historically these were outside of the house. The cyclone is the Southern Hemisphere’s version of a hurricane.
Person who empties the dunny. The dunny was an Australian slang word for an outhouse or toilet tank which was used when there was no septic system or sewer to dispose of human waste.
The person in question is of such incompetence or stupidity they indeed couldn't train a choko vine to grow up a dunny wall. Commonly used to refer to a dim workmate or acquaintance.
The choko (also known as a cheyote or chouchou, among others) being an extremely hardy vine fruit that, left to its own devices, will grow up virtually any surface.
The paperwork's wrong again! Honestly, that moron couldn't train a choko vine to grow up a dunny wall!