to direct liquid jets issuing therefrom against the surface 36 on the guide ring 34 the lower end of wall 44 turns inwardly to provide a transverse wall 50 on the cup shaped plug member 40 what has thus far been described are construction features for aerators that are disclosed in u s pat no 3 684 191 the improvement features of the instant invention will now be described in the form of invention shown in fig1 and 2 the plug member 40 is formed as an annulus having a relatively large central flow opening 52 through its downstream transverse wall 50 the opening 52 is bounded by a downstream cylindrical bore and an adjacent upstream inclined seat 56 that tapers downwardly and inwardly a shape retaining washer 58 molded of plastic preferably polyethylene is positioned above coplanar surfaces 38 and 46 respectively of guide ring 34 and plug member 40 the shape retaining washer 58 is supported at least upon the annular support edge 38 of guide ring 34 but as shown the outer annulus 60 of washer 38 also overlies and engages a portion of surface 46 of plug member 40 the washer 58 has radially spaced outer and inner concentric annular lands respectively 60 and 62 joined together by four circumferentially spaced radial lands 64 the inner annular land 62 surrounds and defines a central flow passageway 66 the annulus between the outer and inner lands 60 and 62 has provided therein a plurality of circumferentially spaced primary flow passageways 68 that are shown to be of arcuate generally oval shape and through which initial flow of liquid is directed downstream in a manner to flush against scrub and dislodge from the slots 48 any debris that may have become lodged therein the debris that is flushed.