A biliary catheter is a small flexible, rubber tube placed into the common bile duct, the passageway for the bile to flow from the gallbladder and liver to the duodenum (small intestine, also referred to as the bowel). The catheter can drain the bile either internally (inside your intestines) or externally (into a bag outside your body). Bile is a thick fluid, usually golden yellow in color.You may have a blockage of the bile ducts, causing the bile to back up into your liver.There may be a hole in the bile duct causing bile to leak.