Abstract: An accumulating whistling vent for indicating a level of liquid in a tank having a vent line is disclosed. The whistling vent includes a whistle housing reservoir which has mounting tubes extending from either ends. A whisle is housed in the whistle housing reservoir by insertion into one of the mounting tubes. The whistling vent is coupled between the vent line of the tank such that the tube containing the whistle is closest to the tank. As liquid is introduced into the tank an audible signal is produced by the whistle. Once full, air flowing from the tank through the vent line is replaced by the incoming liquid, thus muting the whistle. Excess liquid is accumulated in the reservoir prior to discharge from the vent line, thereby providing additional time to respond to the change in audible signal. In a preferred embodiment of the invention, a transparent reservoir is used to provide a visual indicator in addition to the change in audible signal.