Abstract: An apparatus is provided for fumigating waste waters in a fumigation tank with fumigation enclosures (gas manifolds which are situated in parallel next to one another and at a distance from one another and rest horizontally, in whose upper sides gas outlet openings are situated and whose undersides are open, wherein mobile rotation bodies rotated by gas flow are situated for cleaning purposes in the gas outlet openings 13 of the fumigation enclosures 14 and the gas outlet openings 13 each have, in a known manner, a central countersunk section 12 enclosing an angle .alpha. of, for example, 90 to 180.degree. underneath and the remaining wall thickness 15 of the gas outlet opening 13 of each countersunk section 12 amounts to 0.5 to 2 mm. The rotation body according to the invention may comprise a top section 1 and a base section 3 which are joined to a neck section 2.