By the time the tongue gets a thick white coating you need a tongue scraper, OR

Dip a wet washcloth in baking soda, and gently scrub the tongue. Continue doing this, dipping a new section of the rag in baking soda, and washing the tongue to get rid of all the bacteria that has been sitting on your tongue. Wash the washcloth as soon as you can, don't really want it sitting around.

If you don't take care of this one little problem, every time you swallow you are carrying that bacteria into your system. So wash your tongue as often as it takes. Will also kill bacteria on teeth and help make your mouth alkaline.