Rotary vacuum pumps are used in virtually every research lab, especially those engaged in vacuum science such as electron microscopy and mass spectrometry. In the majority of these situations the exhaust can and should be vented to the outside. Unfortunately, many labs lack this capability. Oil mist vapors emitted from pumps under a load can be quite annoying and may be a potential health hazard. Pumps located in small confined spaces such as microscope rooms, darkrooms, etc. are particularly a problem. Often the manufacturer supplied filters are either inadequate or poorly maintained.