Cleaning a narrow neck

Rinse it every day and wash it properly once or twice a week in warm soapy water.

A bottle brush reaches the bottom. If you don't have one, a spoonful of uncooked rice with warm soapy water, swirled for a minute, does a good job.

For cloudy marks from hard water, soak it for an hour in warm water with a splash of white vinegar, then rinse well.