The KleenOil - Bypass Filters each have a 1/4" port on the lid to accommodate a sample valve for ease of oil sample collection. The one exception is the KU06 Mini Duty Filter Unit which does not have the feature. The Oil Sample Port is a small valve that is installed in the lid and opened by attaching a Sample Tube and Cap. By tightening the cap down which opens the valve and allows oil to flow from the dirty oil side of the filter. This oil is collected in an oil analysis bottle and when full the cap is loosened to stop the flow. When the Sample Tube is removed a dust cover is attached to the Oil Sample Port and should be utilized to keep the sample port clean. The Oil Sample Port and the Sample Tube as shown below are sold separately.