For a bit of fizz and to freshen up your drains try mixing half a cup of baking soda with quarter of a cup of salt and pour it down the drain. Follow that with a cup of warm vinegar. That will froth and bubble. Leave it for about 15 minutes and then flush it down the drain with some hot water. If that doesn't do the trick, contact a licensed plumber. They will have the tools and knowledge to clear your drain with ease.