A tank assembly is provided for a machine. The tank assembly may have a tank with a plurality of sides connected to each other to substantially enclose a volume. A first side of the plurality of sides has an upper surface and a lower surface, and defines an opening into the volume and a first rotational stop feature at the opening. The tank assembly may also have a mounting flange with an upper member configured to engage the upper surface of the first side, a lower member configured to engage the lower surface of the first side, and a second rotational stop feature. The tank assembly may additionally have a resilient member disposed between the tank and the mounting flange. The resilient member may be configured to substantially seal an interface between the tank and the mounting flange and to bias the second rotational stop feature toward the first rotational stop feature.