A funnel gag consists of a funnel with a tube leading from its spout into the mouth, usually with straps to hold the tube in. Such a gag is used to force the bound person to drink something (often the dominant's urine). A variant of the funnel gag is the urinal gag (or hood) which effectively turns the wearer into a human urinal.
Warning: It is very easy to choke during such forced drinking. For issues regarding the consumption of urine, read the article on watersports.