An exhaust system for a liquid processing vessel or tank including a port provided in a cover of the tank and a closure fixed in the tank to close the port when the cover in a closed position closing the space enclosed by the tank. The cover is movable to an open position and fumes or vapors from the liquid in the tank are removed through the port and a conduit communicating with the port and an exhaust passage in which suction is produced to remove the vapors. When the cover is moved to its closed position closing the tank to allow processing of the liquid, the closure blocks the port in the cover.
