Blakemore tubes (and their analogues like Minnesota tubes) are rarely used in the modern day of endoscopy but can still have a role in the acute setting of gastrointestinal bleeding from varices. These tubes are lubricated and passed to roughly 50 centimeters in the same manner as an orogastric or nasogastric tube. I prefer the orogastric to avoid compounding a GI bleed with a nose bleed. Ideally, they are also placed with a secure airway.
The gastric balloon is then inflated with air (up to 500 cc), and a traction weight (1-2 pounds) is applied on the outside of the tube to pull this balloon snugly against the gastroesophageal (GE) junction. This maneuver applies pressure on the GE junction to decrease variceal blood flow. If bleeding persists, the esophageal balloon is slowly inflated using a manometer to periodically check the pressure applied to the esophageal wall. Typically 30-45 mmHg is initially inflated and slowly reduced over the course of hours to avoid pressure necrosis of the esophageal mucosa. Depending on the specific tube (ie, Blakemore, Minnesota, etc), aspiration ports are located in the esophageal and gastric regions too.
Oh yeah, and make sure the GI service is already aware of the patient since these Blakemore tubes are just temporizing measures.