a storage container having a fluid inlet;

a cap for sealing the fluid inlet, wherein the cap comprises an aperture in a surface of the cap and a lid for releasably sealing the aperture;

an adapter for releasably connecting the cap to a fluid outlet coupling port of a fluid sampling device, the fluid sampling device being configured to collect a fluid sample from a vehicle or machine, wherein the adapter comprises a body having an internal lumen extending longitudinally between inlet and outlet apertures of the body, wherein the inlet aperture of the body is configured to engage fluidly with the fluid outlet coupling port, and a connector assembly for fluidly connecting the outlet aperture of the body to the aperture in the cap, wherein the surface of the cap and a lowermost end of the body are mutually adapted to provide an airtight seal therebetween when the adapter and cap are connected together by the connector assembly;

a penetrable diaphragm disposed inside the cap or the storage container that provides an airtight seal over a storage region of the storage container below the penetrable diaphragm, wherein the penetrable diaphragm has one or more premade perforations therein, wherein the one or more premade perforations provide a plurality of elastically bendable flaps for receiving, through the penetrable diaphragm, a fluid outlet tube of the fluid sampling device to receive the fluid sample into the storage region;

an annular channel provided in the surface of the cap that extends around the aperture of the cap; and

an annular ridge that protrudes downwardly from an underside of the lid that is adapted to engage into the annular channel when the lid is closed,

wherein the cap and adapter are mutually dimensioned such that the fluid outlet tube extends through the aperture of the cap and protrudes through the flaps into the storage region when the adapter is connected to the fluid outlet coupling port and when the cap is connected to the adapter.