A sterilization apparatus is disclosed for sterilization of objects. The sterilization apparatus includes a chamber for receiving the objects, the chamber including a sterilization medium inlet and outlet； an inlet flow control device for controlling a supply of a sterilization medium to the chamber； a drain system for controllable discharge of fluid from the chamber； and a control unit configured to control the inlet flow control device and drain system in accordance with a sterilization scheme. The drain system includes: a drain inlet connected to the sterilization medium outlet； a drain outlet connected to a vacuum system for evacuating the chamber； a first conduit connecting the drain inlet and outlet； and a proportional valve, arranged along the first conduit, controllable by the control unit to partly restrict fluid flow through the first conduit according to a continuous relation between a control parameter and a valve opening of the proportional valve.
