Abstract: A safety tank for hazardous fluids having a check valve is provided with a filler pipe inserted through a grommet providing a passage for fluids to the interior of the tank. A check valve integral with the grommet prevents reverse flow of the fluid out of the tank as might occur in an accident where the filler pipe or cap is forcibly removed. The tank can be applied to various uses, and existing tanks can be modified by the inclusion of a check valve to encompass the safety features of the present invention. Other embodiments of the tank are provided that include check valves which fit various tank inlet configurations.