Suction device and process for at least one of conditioning and drainage of an endless felt. The device includes a housing having at least one vacuum chamber, and a plurality of suction slits located on a suction surface of the housing that is adapted to face the endless felt. The plurality of suction slits are oriented to extend at least one of in and obliquely to a travel direction of the endless felt. The process includes guiding the endless belt over a suction surface of a vacuum chamber, and suctioning a surface of the endless belt with a plurality of suction slits located in the suction surface of the vacuum chamber. The plurality of suction slits extend in a direction that is at least one of in and oblique to a belt travel direction.