The utility model relates to a do benefit to drainage device that catchments who keeps watch on operation conditions, the row water outlet of the water pipe's who establishes at the desiccator unit below, the desiccator unit decreases desiccator and post -filter including leading filter, zero gas that connects gradually, the drainage device that catchments is transparent hollow cuboid, catchment drainage device's top and connect the drain pipe that leading filter, zero gas decreased desiccator and post -filter respectively. Compared with the prior art, the utility model discloses in concentrating drain pipe of each device of desiccator unit on the drainage device that catchments, observing the drainage situation when workman of being convenient for patrols and examines directly perceivedlyand observing the water level, help judges whether normal catch water is, can in time get rid of the dangerous situation.