A funnel gag is an extreme type of gag rarely found outside of BDSM. A funnel gag is most similar to a muzzle gag, as it is extensively and tightly corrected. Ironically, it is one the least effective gags for silencing a submissive, as the exposed tube allows the wearer to make booming noises. And adding more features to keep the subject quiet only defeats the purpose of the funnel.
This type of gag is designed to allow the dominant to force the wearer to drink whatever fluid they choose. Since the tube of the gag ends behind the teeth and over the tongue, it is impossible to resist. Commonly, urine is used because it completely humiliates the subject. Funnel gags are also amongst the most dangerous, as the subject may experience choking and be unable to signal for a pause. Funnel gags are also difficult to correctly improvise, and thus only used in advanced BDSM sessions.