The respiratory tract, the lungs and bronchi, mainly evacuates toxins in the form of carbonic gas. It may also excrete phlegm.
Healthy membranes of the alveoli do not let solid waste penetrate. However, due to constant irritation by infectious microbes and other irritants, the alveoli may become porous and act as an emergency exit for toxins that the liver, kidneys and the intestinal tract did not succeed in eliminating.
These substances are transported by the blood stream towards the lungs and bronchi, they squeeze through the alveoli and we cough them up as phlegm.
This phlegm not only consists of microbes and the products of their activity, but also of waste resulting from insufficient digestion and excretion.