A tank filling device for a liquid container has a base body with mounting end to secure the base body on a liquid container. An actuating section is disposed in the base body interior and slidable lengthwise relative to the base body. A liquid valve is connected to an outlet opening for liquid and controls the outlet opening by being coupled to the actuating section such that the liquid valve is manually opened or closed by moving the actuating section. An air channel with air inlet and air outlet supplies air into the liquid container for pressure compensation. The air channel extends from the liquid valve toward the mounting end and has an air valve at the air outlet. The air outlet is provided between the actuating section and the base body and is a slot control valve formed by actuating section and base body.