1. If you use it, you wash it.
2. If you cook with it, no matter who eats what was made, by exercising the free will to choose to cook, you wash it.
3. If you cook something, and put the leftovers into tupperware… here’s where it gets tricky. In this case, it does not matter who has cooked the food inside, but whoever cleans out those contents is responsible for washing said tupperware.
I have found that this last rule is a big determiner of portion control for me.
music: Franz Liszt - La Campanella