The invention concerns devices for emptying, in an ambient milieu where there prevail a pressurised atmosphere and gravitational force, a container of viscous liquid. Said device is essentially characterised in that it comprises a receptacle (1) with a main volume (2) including two parts, one higher (3) and one lower (4), wherein a separation wall (5) delimits two secondary volumes (6, 7), an orifice (8) provided in the wall (5) to communicate the two secondary volumes (6, 7) and emerging in the secondary volume (7) in the main volume higher part (3), a pump (10) mounted co-operating with the receptacle (1), its suction inlet (11) being in the volume (6) and its outlet (12) emerging outside the receptacle (1), a branch pipe (14), and means (17) for mounting the branch pipe (14) in association with the receptacle (1) such that the outlet duct (16) is located in the secondary volume (7) and the inlet duct (15) is outside (13) the receptacle (1). The invention is particularly useful for changing oil in cylinder blocks of motor vehicles or the like.