A filter device for a conduit includes a gas-permeable pre-filter element and a gas-permeable, liquid-impermeable filter element. The filter device is configured to be fluidly coupled to a conduit such that a gas can flow, in sequence, through the pre-filter element, the filter element and then the conduit. The filter device can be used in each of a vehicle hollow driveshaft and a hollow wheel stub axle forming a CV joint having a compressed air supply line which passes therethrough. Compressed air can be supplied via the air supply line without the need for an additional fluid transfer device fluidly connecting the driveshaft and the stub axle's conduits.