A system for evacuating an enclosure is provided. The system includes a first vacuum pump having an inlet selectively connectable to an outlet from the enclosure. A second vacuum pump is also provided together with a conduit for connecting an exhaust of the first vacuum pump to an inlet of the second vacuum pump. An auxiliary chamber is provided, this chamber being selectively connectable to the conduit such that, in a first state, gas can be drawn from the auxiliary chamber by the second vacuum pump in isolation from the enclosure, and, in a second state, gas can be drawn from the enclosure to the auxiliary chamber through the first vacuum pump.