Disclosed is a device for evaporating vapors of a fuel stored in a motor vehicle tank. The evaporation device includes a bypass circuit and a bypass valve configured to move between a so-called “absorption” position, in which the bypass valve allows the gases to flow between the tank and an absorbent filter and a so-called “leak detection” position, in which the bypass valve allows the gases to flow between a purge circuit and the tank via the bypass circuit.