A glass U-shaped outlet for a reactor setup, often a bottom discharge valve or specialized drain tube, is critical for low-dead-volume drainage in jacketed or plain glass reactors, typically using Borosilicate 3.3 glass for chemical resistance and thermal shock resistance. These systems often utilize PTFE or KF flanges for a leak-tight, self-draining seal, ideal for batch-to-batch processing. 

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This video shows a glass reactor setup with a bottom valve: