Abstract: A device is provided for sampling the contents of a pressurized circulating fluid system of a machine. The device is incorporated in a parallel fluid circuit and comprises a housing with an inlet to, and outlet from, a cavity. A filter is received within the cavity. When the filter becomes clogged, a differential pressure sensor provides an indication for an operator to close the inlet to the filter cavity, drain the cavity by means of a valve, and then remove the filter by removing a plug. The drained cavity fluid and filter may then be shipped to a lab for testing and the filter replaced and the inlet to the cavity reopened.