Abstract: A vacuum unit, intended particularly for a vacuum toilet system, includes two valves (4, 6) which can be connected to a compressed-air source, an ejector (10) which includes an inlet nozzle (10a), an outlet nozzle (10b) and a vacuum opening (10c). The ejector is connected to the first valve (4) via the inlet nozzle, and to a first vacuum-unit connection (U1), via the vacuum opening. A piston valve (16) includes a first inlet (16a), a second inlet (16b) and an outlet (16c). The first inlet connects the piston valve with the ejector outlet nozzle (10), the second inlet connects the piston valve with the second valve (6), and the outlet connects the piston valve with a second vacuum-unit connection (U2). A check valve (17) is mounted between the piston valve outlet (16c) and the second vacuum-unit connection (U2). A passageway connects the second valve (6) and the second inlet (16b) of the piston valve with a further ejector inlet (10d).