Anti-slosh device in fuel tank

In a device for reducing fuel sloshing in a fuel tank (1) of a motor vehicle, an anti-slosh element (2) is designed to be movable from a mounting position, in which it can be installed through a mounting opening of the fuel tank (1), into an operating position, in which it is locked with the wall of the fuel tank (1). The anti-slosh element (2) can therefore be simply installed. The fuel tank (1) is particularly simply constructed.