Refill your birdbath with clean water every day, or at least every other day. Fresh water can help to prevent the growth of algae.
Drain the water from the birdbath approximately every three days to a week. You can usually tip the bowl of the bath to drain it, although some baths actually have plugs that can be removed for drainage.
Clean the birdbath by scrubbing it with a stiff, nylon-bristled brush.
Add a teaspoon of gentle dish soap or birdbath cleaner (from a pet store or pet supply company) if the slime and dirt can't be removed with water and brushing alone. Scrub the soap or cleaner around the bowl to remove heavy slime and debris.
Rinse thoroughly, especially if you used any type of soap or cleaner.
Refill the bath with fresh water.