Gary:
I think you're getting an endoscopy and a barium swallow confused.
For an endoscopy you don't drink any specific liquid, the doctor uses a long flexible tube to look at your throat and esophagus on a TV monitor (or through an eyepiece). You'll probably be sedated because the procedure can be uncomfortable.
For a barium swallow you drink the chalky liquid (barium sulfate) and the doctors will take a series of x-rays that help them see what's going on in your upper GI tract.
