A flush valve arrangement for use in a vacuum toilet system, the flush valve arrangement comprising: a vacuum toilet waste receptacle supported by a toilet stand, which has an integral flush valve side panel; a flush valve incorporated in the side panel, which side panel includes a housing having an outlet port which is connected to a vacuum source comprising a vacuum generator in fluid communication with the outlet port, the outlet port being aligned with and in selectable fluid communication with a corresponding inlet port, the inlet port being in fluid communication with the vacuum toilet waste receptacle for receiving waste therefrom; a discharge disk mounted in the side panel and including a rotary section and a continuous covering section, the covering section being aperture-free and continuous and of a size and shape corresponding to a size and shape of the single outlet, the rotary section being mounted to the side panel for rotary movement of the discharge disk between a closed position in which the covering section seals the outlet from fluid communication with the inlet and an open position in which the entire covering section is substantially clear of the outlet; and a sleeve seal disposed in the side panel between the outlet and the discharge disk, the sleeve seal abutting the perimeter of the outlet to seal the outlet when the discharge disk is in the closed position; a drive assembly mounted on the side panel and comprising gearing for rotating the discharge disk between the closed position and the open position in response to a driving force applied to the gearing, the drive assembly including an actuator shaft mounted on the flush valve, a follower gear mounted on the flush valve and adapted to rotate the discharge disk, a driver gear mounted on the actuator shaft and adapted to rotate the follower gear, and an extension arm integral with the driver gear for manually opening the flush valve; and a motor operatively connected to the drive assembly, characterised in that the discharge disk is tear-shaped and the rotary section is at the narrower trailing portion of the tear-shape and the covering section is at the wider leading portion of the tear-shape. a vacuum toilet waste receptacle supported by a toilet stand, which has an integral flush valve side panel; a flush valve incorporated in the side panel, which side panel includes a housing having an outlet port which is connected to a vacuum source comprising a vacuum generator in fluid communication with the outlet port, the outlet port being aligned with and in selectable fluid communication with a corresponding inlet port, the inlet port being in fluid communication with the vacuum toilet waste receptacle for receiving waste therefrom; a discharge disk mounted in the side panel and including a rotary section and a continuous covering section, the covering section being aperture-free and continuous and of a size and shape corresponding to a size and shape of the single outlet, the rotary section being mounted to the side panel for rotary movement of the discharge disk between a closed position in which the covering section seals the outlet from fluid communication with the inlet and an open position in which the entire covering section is substantially clear of the outlet; and a sleeve seal disposed in the side panel between the outlet and the discharge disk, the sleeve seal abutting the perimeter of the outlet to seal the outlet when the discharge disk is in the closed position; a drive assembly mounted on the side panel and comprising gearing for rotating the discharge disk between the closed position and the open position in response to a driving force applied to the gearing, the drive assembly including an actuator shaft mounted on the flush valve, a follower gear mounted on the flush valve and adapted to rotate the discharge disk, a driver gear mounted on the actuator shaft and adapted to rotate the follower gear, and an extension arm integral with the driver gear for manually opening the flush valve; and a motor operatively connected to the drive assembly, characterised in that the discharge disk is tear-shaped and the rotary section is at the narrower trailing portion of the tear-shape and the covering section is at the wider leading portion of the tear-shape.