A draining arrangement of a propulsion unit such as an azimuthing propulsion unit of a marine vessel, the propulsion unit comprising a shell structure mounted below a hull of the marine vessel such that the shell structure is at least partly immersed in water, when the marine vessel floats in water, wherein the shell structure limiting at least one bottom section configured to receive liquids formed within the shell structure and/or liquids entering the shell structure from the outside of the shell structure, and wherein the draining arrangement comprising a pneumatically operated drainage arrangement in fluid connection with said at least one bottom section, wherein the pneumatically operated drainage arrangement is configured to at least partly drain said at least one bottom section and to transfer liquid from said at least one bottom section to a collector arrangement provided within the hull of the marine vessel, characterized by the pneumatically operated drainage arrangement comprises an intermediate tank within the shell structure, wherein the intermediate tank is located at a vertical level that is above said at least one bottom section, a pressurizing arrangement functionally connected to the intermediate tank and configured to selectively provide a vacuum in the intermediate tank or an excess pressure in the intermediate tank, a first liquid line that is provided between the intermediate tank and said at least one bottom section, wherein the first liquid line is provided with a first check valve configured to prevent liquid to flow from the intermediate tank to said at least one bottom section and configured to allow liquid to flow from said at least one bottom section to the intermediate tank, and a second liquid line that is provided between the intermediate tank and the collector arrangement within the hull of the marine vessel, wherein the second liquid line is provided with a second check valve configured to prevent liquid to flow from the collector arrangement provided within the hull of the marine vessel to the intermediate tank and configured to allow liquid to flow from intermediate tank to collector arrangement provided within the hull of the marine vessel. wherein the shell structure limiting at least one bottom section configured to receive liquids formed within the shell structure and/or liquids entering the shell structure from the outside of the shell structure, and wherein the draining arrangement comprising a pneumatically operated drainage arrangement in fluid connection with said at least one bottom section, wherein the pneumatically operated drainage arrangement is configured to at least partly drain said at least one bottom section and to transfer liquid from said at least one bottom section to a collector arrangement provided within the hull of the marine vessel, characterized by the pneumatically operated drainage arrangement comprises an intermediate tank within the shell structure, wherein the intermediate tank is located at a vertical level that is above said at least one bottom section, a pressurizing arrangement functionally connected to the intermediate tank and configured to selectively provide a vacuum in the intermediate tank or an excess pressure in the intermediate tank, a first liquid line that is provided between the intermediate tank and said at least one bottom section, wherein the first liquid line is provided with a first check valve configured to prevent liquid to flow from the intermediate tank to said at least one bottom section and configured to allow liquid to flow from said at least one bottom section to the intermediate tank, and a second liquid line that is provided between the intermediate tank and the collector arrangement within the hull of the marine vessel, wherein the second liquid line is provided with a second check valve configured to prevent liquid to flow from the collector arrangement provided within the hull of the marine vessel to the intermediate tank and configured to allow liquid to flow from intermediate tank to collector arrangement provided within the hull of the marine vessel.