The utility model provides an exhaust, which comprises an infusion pipeline with a liquid inlet and a liquid outlet, and an exhaust duct which is communicated with the infusion pipeline. When a vacuum filter is used for injecting insulating oil into an electric transformer, the exhaust provided by the utility model can exhaust the air existing in the body and an oil tube of the vacuum filter via the exhaust duct, consequently, the air is prevented from entering the vacuum cavity of the electric transformer along with the insulating oil, so that the electric transformer cannot be insulated and damped, and the quality of oil injection is remarkably increased.