Just to clarify, I'm not talking about the Lush product of the same name.
In Australia, the washing up fairy is a mythical creature. People leave their dishes unwashed overnight, and lo and behold, the next morning the dishes are clean thanks to the washing up fairy.
Sadly, she (I assume it's a she) is more often noted in her absence than her presence. As in "The washing up fairy didn't come, I'll have to do the dishes now."
An example of her being mentioned:
Her theory is simple – we must replace the behaviours we don’t want with those we do. For example, leaving dirty dishes on the kitchen bench for the washing-up fairy to tidy should be replaced with loading the dirty dishes in the dishwasher.
Her existence has been documented neither by Wiktionary nor Urban Dictionary.
Is her distribution limited to Australia, and presumably New Zealand, plus the households of those who have moved from these countries?