A cassette for collecting tissue samples from a fluid stream, said cassette comprising: a body , the body having: a fitting for receiving a suction line through which fluids are drawn away from a patient; an outlet opening through which a suction is drawn; a tray-receiving void between the fitting and the outlet opening, the void being in a fluid path with the outlet opening; and a bypass conduit between the fitting and the outlet opening, the bypass conduit forming a bypass fluid path around the void ; a catch tray removably mounted in the tray-receiving void , the catch tray adapted to allow fluid flow therethrough into the outlet opening while retaining material above a certain size that is entrained in the fluid flow through the catch tray; and a valve movably mounted to the body to receive the fluid drawn into the fitting , the valve adapted to directed the fluid flow from the fitting into either the bypass conduit or the tray-receiving void , characterized in that : the cassette body is formed with an exposed face and comprises plural tray-receiving voids that extend inwardly from the exposed face; the cassette comprises separate catch trays each removably mounted in one of the tray-receiving voids such that each catch tray is independently removable from and reinstallable in the tray-receiving void in which the catch tray is held; and the valve is configured to direct the fluid flow from the fitting into either the bypass conduit or any one of the tray-receiving voids receiving a respective one of the separate catch trays. a body , the body having: a fitting for receiving a suction line through which fluids are drawn away from a patient; an outlet opening through which a suction is drawn; a tray-receiving void between the fitting and the outlet opening, the void being in a fluid path with the outlet opening; and a bypass conduit between the fitting and the outlet opening, the bypass conduit forming a bypass fluid path around the void ; a catch tray removably mounted in the tray-receiving void , the catch tray adapted to allow fluid flow therethrough into the outlet opening while retaining material above a certain size that is entrained in the fluid flow through the catch tray; and a valve movably mounted to the body to receive the fluid drawn into the fitting , the valve adapted to directed the fluid flow from the fitting into either the bypass conduit or the tray-receiving void , characterized in that : the cassette body is formed with an exposed face and comprises plural tray-receiving voids that extend inwardly from the exposed face; the cassette comprises separate catch trays each removably mounted in one of the tray-receiving voids such that each catch tray is independently removable from and reinstallable in the tray-receiving void in which the catch tray is held; and the valve is configured to direct the fluid flow from the fitting into either the bypass conduit or any one of the tray-receiving voids receiving a respective one of the separate catch trays. the cassette body is formed with an exposed face and comprises plural tray-receiving voids that extend inwardly from the exposed face; the cassette comprises separate catch trays each removably mounted in one of the tray-receiving voids such that each catch tray is independently removable from and reinstallable in the tray-receiving void in which the catch tray is held; and the valve is configured to direct the fluid flow from the fitting into either the bypass conduit or any one of the tray-receiving voids receiving a respective one of the separate catch trays. <EOS>