Valve, Chem-Drain, 12mm, Complete with Glass Body, TFE Stem and Control Knob. Valve, Chem-Drain, 6mm, Complete w/ Glass Body, TFE Stem & Control Knob. The design of the Chem-Drain valve incorporates a PTFE plunger that allows the contents of the flask to drain directly through the bore of the plunger. When closed, the tip of the PTFE plug seals into the lower radius of the flask. This feature permits total mixing and drainage of the contents of the flask. When open, the contents of the flask drain through three openings into the main bore of the plug. Lower portion of the plunger has a 18mm section on the 12mm size for attachment of flexible tubing to allow material to be transferred into a receiving vessel. The 12mm size will allow drainage of solids to 2mm diameter. When ordered complete, the valve comes w/ a glass barrel, PTFE stem & black Acetal control knob.