The unit has pump unit housing (1) provided with a front wall (11), a rear wall (10), and a sidewall (16) which are arranged between two walls. The front wall and the rear wall are each fitted with one wall edge that protrudes from the sidewall, the fluid collecting vessel (2) being retained between said wall edges such that the fluid collecting vessel is easy to attach to the pump unit housing while being retained. An independent claim is also included for a fluid collecting vessel for retaining sucking body fluids.
