A good herb to cleanse the lungs is lobelia leaf. It causes the lungs to expel toxins and mucus and is a purgative. The American Indians used the herb to treat respiratory and muscle disorders. Today it is also used to treat asthma and food poisoning. The herb relaxes muscles and can be smoked to help people quit tobacco addictions. The herb is also known as Indian Tobacco, Asthma Weed, Pukeweed, or Vomitwort.
Lobelia is also an ingredient in many detox and cleansing programs (
http://www.detox.net.au/articles/colon-cleanse/cleanse-kit-reviews/), including the famous Arise and Shine cleanse by Richard Anderson (
http://www.detox.net.au/Cleansing-body-transition-Detox-Diet-Cleanse-Recipes.htm). The herb apparently has extremely powerful anti-cancer properties and it is illegal to sell it in Australia for therapeutic reasons.
Lobelia is a common household flower and can be purchased from most nurseries. The normal dose per day is 1/2 to one leaf.