Mouthpiece (bong)

A mouthpiece (no. 1 at the picture) is a component of bong, where the users mouth is placed over, sealing out air through that hole. Thus the bong is airtight (providing there is also an airtight seal around the stem. If a carb is present, it must also be covered). When airtight it has but one small source of air, which comes into effect when the user inhales through the mouth piece. If all the smoke isnt removed from the bong in a single hit, the user can place their mouth again over the bong to again inhale, or hover their mouth closely over the bong to slowly inhale the smoke.