Abstract: A tank vent cap for seating on the gas exhaust or vent pipe of a tank such as a sewage treatment system tank and preventing entry of rainwater, debris or animals into the pipe while facilitating the escape of gas, typically air, from the pipe. In a preferred embodiment, the tank vent cap is characterized by a cylindrical cap wall having inside, radially spaced-apart vent indentations formed therein and fitted with tabs located on the underside of the cap top. When the cap is placed on the air exhaust or vent pipe, the tabs of the cap engage the top edge or lip of the pipe to define top air passages between the pipe lip and the underside of the cap top. The vent indentations define side air passages between the outside surface of the pipe wall and the inside surface of the cap wall, which side air passages communicate with the top air passages. The tank vent cap can be quickly and easily removed and replaced on the pipe in a friction-fit, without the use of bolts or other fasteners.