I’m going to list these in order of preference. Each is single use to about 3 cups water.
2 Tablespoons powdered sugar
2 Tablespoons lemon juice
1 aspirin (ground)
OR
2 Tablespoons vinegar
2 Tablespoons sugar
OR
1 Tablespoon sugar
1/4 teaspoon bleach
OR
4 Tablespoons lemon-lime soda
1 very small drop of bleach